zero (number) / (informal) Used to refer to something measurable being absent or missing.

a theory

Russia

The katakana syllable ロ (ro). Its equivalent in hiragana is ろ (ro). It is the forty-third syllable in the gojūon order; its position is ラ行オ段 (ra-gyō o-dan, “row ra, section o”).

short form for Russia or Russian, Russo- (prefix), short form of ロシア (Roshia), also written in kanji: 露 (ろ, Ro).

si (musical note)

hearth, fireplace (open recess in a wall at the base of a chimney)

dream, ideal / a novel / romance

reasoning, line of thinking

a traffic route, a train line / a course which companies or groups have for a purpose