the Quaternary period

a Classical Japanese adjective with ク活用 (ku-katsuyō, “ku-inflection”)

safety first

third party, outsider

(education) second year in senior high school; eleventh grade / (education) second-year student in senior high school

(shogi) two pawns on a same file (an illegal move)

the second dimension / (by extension, Internet slang) the 2D (i.e. anime, manga, video games, etc.) world; the fictional world

A city in Iwate Prefecture, Japan, Asia / A district of Iwate Prefecture, Japan, Asia

number two / runner-up

(Internet slang) opening 2 different windows (chatroom, etc.) at the same time