On what subject?
По какой теме?
subject catalogue - предметный каталог
delicate subject - щекотливая тема
to subject smb. to discrimination - дискриминировать кого-л., подвергать дискриминации
dull subject - скучная тема
be subject to a rule - подчиняться правилу
subject complement: a word or a group of words, usually functioning as an adjective or noun, that is used in the predicate following a copula and describes or is identified with the subject of the sentence, as sleepy in The travelers became sleepy
drop the subject/drop it/let it drop: If you want someone to drop the subject, drop it, or let it drop, you want them to stop talking about something, often because you are annoyed that they keep talking about it.