full-fledged, qualified, up to standard / adulthood, behaving like an adult or as a member of the society / Used other than figuratively or idiomatically: see 一人, 前. ("one person's portion")

a (single) meal / a (single) bowl of rice

One slice or cut of something.

a (single) leaf / (figuratively) a (single) small boat / a (single) sheet (something thin: page, etc.)

a (single) blast of air (wind, etc.)

a male given name

(alcoholism) Synonym of 一杯 (ippai, “one cup”) / (alcoholism) drinking

to start again from scratch

(informal) last one remaining (as of an item at the store, etc.)

trouble (distressful or dangerous situation)