四

From Confucius

at age forty, one has no doubts

Mathematics

four-color theorem; four-color map theorem

Idiomatic expression

The world is at peace

quartile

the four grand national holidays (Prayer to the Four Quarters, Empire Day, the Emperor's Birthday, Emperor Meiji's birthday; 1927-1948)

Tetragonocalamus quadrangularis (type of bamboo); Chimonobambusa quadrangularis

Organization name

Shikoku University

enjoying food, drink and entertainment in a small room

the four examinations (in Chinese medicine: seeing, hearing, asking, touching)

fourth tray (of food)

people in the whole world being all brothers; universal brotherhood

tesseract

Buddhism

four gratitudes (to one's parents, all living beings, one's sovereign and the Three Jewels); four obligations

Mahjong

winning hand consisting of four kongs and a pair

Linguistics; じ,ぢ,ず,づ

yotsugana; the four kana (ji, di, zu, du)

four-letter word (vulgar English term, e.g. fuck)

Abbreviation; Buddhism

four types of mandala (in Shingon)

Russian tortoise (Agrionemys horsfieldii); Horsfield's tortoise; Central Asian tortoise; steppe tortoise; four-toed tortoise

wooden plane with a convex base curved both along the direction of cutting and across the blade

silicon tetrachloride (SiCl4)

(emblem of) four comma-shaped figures arranged to form a circle

four-way fight; four-sided struggle

elegant classical Chinese prose employing antitheses using four and six-character compound words

Physics

four velocity

quadrant