a male given name

one letter, one character

(idiomatic) unhesitatingly without dispute

(grammar) The monograde verb conjugation class, consisting of the two subclasses of 上(かみ)一(いち)段(だん)活(かつ)用(よう) (kami ichidan katsuyō, “upper-monograde conjugation”) and 下(しも)一(いち)段(だん)活(かつ)用(よう) (shimo ichidan katsuyō, “lower-monograde conjugation”)

(military) captain (Japanese Air Self-Defense Forces, Japanese Ground Self Defense Forces) / (military) lieutenant (senior grade) (Japanese Maritime Self-Defense Force)

city

一部: part / 一分: one minute; a few

一流: first class

一日, 1日: one day

一事不再理: the principle against double jeopardy(exceptio res judicata).