the numeral 4

(animal legs) + (mouth/small box radical)
★★★★★
5 strokes
ABU
Along with '7'、 '4' is one of the numbers where the KUN and ON are used pretty randomly.
Like, more than usual.
For example, when counting months, usually one uses the ON-yomi, but with 4 and 7 you use the KUN-yomi!

ABU: since this has the same ONyomi as 'death' (死) it is considered an unlucky number.

Onyomi

SHI

Mnemonic

SHE can fit four legs in her mouth at the same time. (FYI she is not kinky, she is a female Carcharodon carcharias)

Kunyomi

よ*つ 4 things COUNTER
★★★★★

Jukugo

四月(しがつ)

April ★★★★★ FPKANA
(the numeral 4) + (moon) = 四月 (April)

四時(よじ)

4 o'clock ★★★★★
(the numeral 4) + (time) = 四時 (4 o'clock)

四時間(よじかん)

4 hours' time ★★★★★
(4 o'clock) + (a period of time) = 四時間 (4 hours' time)

4 hours' time. As in, this bus ride takes 4 hours.

四日(よっか)

fourth day of the month ★★★★☆ FP
(the numeral 4) + (sun, day) = 四日 (fourth day of the month )

四角(しかく)

a square ★★★☆☆
(the numeral 4) + (horn/corner) = 四角 (a square)

Used In