a surname

(history, socialism) the Second International

second party, after-party

a quadratic equation

twelfth day of the month

Used other than figuratively or idiomatically: see 二, 枚, 目. (the second sheet or other flat thing) / a handsome male character, especially one that gets involved in a romance during the story

(taxonomy) binomial nomenclature

(typography) the iteration mark 〻, used to repeat kanji, historically mostly kanji with kun'yomi

double room

(linguistics) doublet