the first day of the month (solar or lunar calendar)

(literary) one day, 24 hours / (literary) the daytime, the period from dawn until dusk / (literary) (figuratively) a short period of time

one week

one month (duration)

eleven; 11

a male given name

a speck; a spot / a little bit

the first / (mathematics, attributive) the quality of being first-degree

Used other than figuratively or idiomatically: see 一 and 本 (one thing) / Short for 一本勝ち (ippon-gachi, “winning in one blow”).

solely / only, simply / alone, automatically, by itself, naturally