Weekdays in Japanese - Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday

In Japan, a week has seven days just like everywhere else in the world (probably). For reference, this is what the weekdays are called in Japanese:

Weekday	kanji	romaji
Sunday	日曜日	nichiyoubi
Monday	月曜日	getsuyoubi
Tuesday	火曜日	kayoubi
Wednesday	水曜日	suiyoubi
Thursday	木曜日	mokuyoubi
Friday	金曜日	kin'youbi
Saturday	土曜日	doyoubi

Source: japanesewithanime.com (CC BY-SA 4.0)

• Morphology
  • First Kanji Meaning
  • Mnemonics
• Usage
  • Abbreviations
    • Multiple Weekdays
    • Between Parentheses in Dates
  • A Day's Weekday
  • What Weekday?
  • Weekend
  • Specifying The Week
    • Deitic
    • Ordinal
• References

Morphology

The words for weekdays are formed by multiple morphemes: the ~youbi ～曜日 suffix that means "weekday" plus a single-kanji morpheme that names that weekday.

Notably, in the word for Sunday, nichiyoubi 日曜日, you have the 日 kanji twice, but with different readings. The nichi 日 reading is an on'yomi 音読み reading which names the weekday, while the ~bi ～日 reading is a kun'yomi 訓読み that's part of the ~youbi suffix.

First Kanji Meaning

The meaning of the first kanji of each weekday appears to be random, but the weekdays are actually named after the seven celestial bodies visible to the naked eye: five "planets," wakusei 惑星, plus the Sun and the Moon.^{(sendai-astro.jp)} Observe:

Single-kanji word.	Celestial Body
nichi 日 Day.	hi (taiyou) 日（太陽） Sun.
getsu 月 Month.	tsuki 月 Moon.
hi 火 Fire.	kasei 火星 Mars.
mizu 水 Water.	suisei 水星 Mercury.
ki 木 Tree.	mokusei 木星 Jupiter.
kin 金 Gold.	kinsei 金星 Venus.
tsuchi 土 Soil.	dosei 土星 Saturn.

Basically humans could see these seven celestial bodies, called shichiyuu 七雄, which they considered to be deities, and they could figure out that a single moon phase lasted seven days, so they imagined each weekday was ruled over by a different space-god, and that's where their names come from.

Finally, you may be wondering why are the planets named like this in Japanese. Why is Jupiter "tree"?

The names of the planets in Japanese come from the Chinese Wuxing (five phases, or "five elements"), which would be fire, water, wood, metal (gold), and earth (soil).^{(eco.mtk.nao.ac.jp:曜日の名前)}

By the way, something similar occurs in English: in imperial Rome, the days of the week were named after the planets, which in turn were named after the roman gods, when these weekday names were borrowed, the Roman god's name was replaced by a comparable Germanic god's name, except for Saturday, which retained its original Roman name.^{(english.stackexchange.com, citing the Oxford English Dictionary)} Observe:

Weekday	Old English	Latin
Sunday	Sunnandæg Day of Sun.	dies Solis Day of Sol.
Monday	Mōnandæg. Day of Moon.	dies Lunae Day of Luna.
Tuesday	Tīwesdæg Day of Tīw	dies Martis Day of Mars.
Wednesday	Wōdnesdæg Day of Odin	dies Mercurii Day of Mercury.
Thursday	Thunresdæg Day of Thunder. Day of Thor.	dies Jovis Day of Jove. Day of Iupiter.
Friday	Frīgedæg Day of Frigga.	dies Veneris Day of Venus.
Saturday	Sæternesdæg Day of Saturnus.	dies Saturni Day of Saturnus.

Mnemonics

If you're having trouble remembering the names of weekdays in Japanese, here are some simple mnemonics:

• Sunday is nichi 日 just like hi 日 is "Sun."
• Moon, tsuki 月, comes after the Sun, i.e. getsuyoubi after nichiyoubi, so getsuyoubi is Monday
• Fire comes before water—kayoubi, suiyoubi.

I don't have a mnemonic for the rest, but you'll probably memorize the names for the Friday and Saturday rather quickly considering they're at the end of the week, so the only thing left will be Thursday. You could try to pretend it's Tree's Day or something to remember it, I guess.

Usage

Every weekday word works as a temporal adverb. They can be used by themselves or followed by the ni に particle.

• kin'youbi suizokukan ni ikimashita
  金曜日水族館に行きました
  Friday, [I] went to the aquarium.
• kin'youbi ni suizokukan ni ikimashita
  金曜日に水族館に行きました
  (same meaning.)

They can also be used as nouns:

• mokuyoubi wa nan'nichi desu ka?
  木曜日は何日ですか？
  Thursday is what day [of the month]?
• mokuyoubi wa ni-juu-ichi-nichi desu
  木曜日は２１日です
  Thursday is the 21st.

Abbreviations

The names for weekdays are often used in abbreviated form. Every weekday, which ends in ~youbi, may be abbreviated so that the ~bi ending is removed and it ends in ~you, or so that the whole ~youbi part is removed. In English something similar occurs, there being a 3-letter representation for every weekday. Observe:

Weekday	Minus ~bi	Minus ~youbi
Sunday SUN	nichiyou 日曜	nichi 日
Monday MON	getsuyou 月曜	getsu 月
Tuesday TUE	kayou 火曜	ka 火
Wednesday WED	suiyou 水曜	sui 水
Thursday THU	mokuyou 木曜	moku 木
Friday FRI	kin'you 金曜	kin 金
Saturday SAT	doyou 土曜	do 土

Generally the entire ~youbi isn't dropped except for specific contexts where it's obvious it's supposed to be a weekday. Dropping the ~bi, however, is rather common.

• kin'you suizokukan ni ikimashita
  金曜水族館に行きました
  (same meaning as before.)

Multiple Weekdays

Sometimes, multiple weekdays may be referred to all at once in single-kanji abbreviated form, sometimes separated by a middle dot (・) in writing, followed by a single ~youbi, like this:

• ka, sui-youbi
  火・水曜日
  Tuesday and Wednesday.
  Tuesday or Wednesday.
• kin, do, nichi-youbi
  金・土・日曜日
  Friday, Saturday, and Sunday.
  Friday, Saturday, or Sunday.

Between Parentheses in Dates

Sometimes when a date is written in Japanese the single-kanji representation of a weekday is written between parentheses at the end, e.g. (土) after a date means it's a doyoubi 土曜日, "Saturday." It's like if (SAT) for Saturday were written.

See also: Japanese Date Format.

Anime: Pop Team Epic, Poputepipikku ポプテピピック (Episode 4, Collage)

• Popuko "Kabedon shitee ❤"
  ポプ子 「カベドンしてェ❤」
  Popuko: "do a kabedon [on me] ❤"
• [ni-sen-]juu-yon-nen juu-ichi-gatsu ni-juu-hachi-nichi (sui)
  １４年１１月２８日（水）
  2014, month 11, day 28, (WED).

A Day's Weekday

The word youbi 曜日 can be used alone to mean the "weekday" of something. For example:

• Context: explaining what a device or computer program does.
• kyou no youbi wo hyouji suru
  今日の曜日は表示する
  [It] displays today's weekday.
• Context: talking about a day in the future when something happen.
• {dono youbi ni} naru ka wakaranai
  どの曜日になるかわからない
  [I] don't know {what weekday} [it] will be.
  • What weekday it will land on.

What Weekday?

To say "what weekday" in Japanese there are two ways:

• dono youbi
  どの曜日
  What weekday. Which weekday of the seven.
• nan'youbi
  何曜日
  What weekday.

For example:

• kyou wa nan'youbi desu ka?
  今日は何曜日ですか？
  What weekday is today?
• mokuyoubi desu
  木曜日です
  It's Thursday.
• teikyuubi wo {nan'youbi ni} suru?
  定休日を何曜日にする
  [You] will make the closing day what weekday?
  • teikyuubi - literally "fixed rest day," in the sense of a day when a store closes that occurs at fixed, regular intervals, e.g. every Sunday.

Weekend

The terms to refer the weekend and days off would be:

• shuumatsu
  週末
  Weekend.
• shuusho
  週初
  Weekstart.
• kyuujitsu
  休日
  Day off. (e.g. the weekend.)
• heijitsu
  平日
  "Ordinary day." A non-holiday. A day in which you work.

In English, sometimes a day that isn't in the weekend is called a "weekday." In this case, "weekdays" would likely translate to heijitsu, because it's in the sense of a day when you work, as opposed to the weekend when you have the day off.

Specifying The Week

Sometimes it's not enough to specify the weekday, it's also necessary to specify which week we're talking about. There are multiple ways to do this.

Deitic

We can refer to a week or weekday relative to today like this:

• konshuu
  今週
  This week.
  • konshuumatsu
    今週末
    This weekend.
  • konshuu no kayoubi
    今週の火曜日
    This week's Tuesday.
• tsugi no kayoubi
  次の火曜日
  Next Tuesday.
• kondo no kayoubi
  今度の火曜日
  (same meaning.)
• raishuu
  来週
  Next week.
  • raishuumatsu
    来週末
    Next weekend.
  • raishuu no kayoubi
    来週の火曜日
    Next week's Tuesday.
• kono mae no kayoubi
  この前の火曜日
  The Tuesday before this. (literally.)
  Last Tuesday.
• senshuu
  先週
  Previous week.
  • senshuumatsu
    先週末
    Previous weekend.
  • senshuu no kayoubi
    先週の火曜日
    Previous week's Tuesday.

For non-immediate weeks:

• isshukan-mae no kayoubi
  １週間前の火曜日
  The Tuesday of one week ago. (previous week's.)
• nishuukan-mae no kayoubi
  ２週間前の火曜日
  The Tuesday of two weeks ago. (the week before the previous.)
• sanshuukan-mae no kayoubi
  ３週間前の火曜日
  The Tuesday of three weeks ago.
• ishuukan-go no kayoubi
  １週間後の火曜日
  The Tuesday of one week later. (next week's.)
• nishuukan-go no kayoubi
  ２週間後の火曜日
  The Tuesday of two weeks later. (the week after the next.)
• sanshuukan go no kayoubi
  ３週間後の火曜日
  The Tuesday of three weeks later.

Ordinal

We can refer to the nth weekday of a month by using dai~ 第～ followed by a number (ichi, ni, san) followed by the weekday, like this:

1. san-gatsu dai ichi kayoubi
   ３月第１火曜日
   The first Tuesday of March.
2. san-gatsu dai ni kayoubi
   ３月第２火曜日
   The second Tuesday of March.
3. san-gatsu dai san kayoubi
   ３月第３火曜日
   The third Tuesday of March.
4. san-gatsu dai yon kayoubi
   ３月第４火曜日
   The fourth Tuesday of March.

References

• 曜日はどうやって決まったの？ - sendai-astro.jp, accessed 2022-07-25.
• Why is “Saturday” Romanic? - english.stackexchange.com, accessed 2022-07-25.
• 曜日の名前 - eco.mtk.nao.ac.jp, accessed 2022-07-25.