World War I

once-in-a-lifetime (event)

safety first

the best or top person, such as the best performer in a company, or a leading expert

(Internet slang) first comment; (interjection) first!

(informal, chiefly in the negative) the slightest amount (in reference to one's knowledge, thought, etc.) / Used other than figuratively or idiomatically: see 一, ミリ.

一月: January / １月: January / 1月: January

小一: first-year student of an elementary school

彰一: a male given name / 正一: a male given name / 省一: a male given name / 章一: a male given name / 松一: a male given name / 詔一: a male given name / 昇一: a male given name

一時: one o'clock / 一字: one letter, one character / 一事: one thing / 一次: first, preliminary