Meaning of SLAG in English

I. slag 1 /slæɡ/ BrE AmE noun

[ Date: 1500-1600 ; Language: Middle Low German ; Origin: slagge ]

1 . [countable] British English taboo informal a very offensive word for a woman who has sex with a lot of different people. Do not use this word.

2 . [uncountable] a waste material similar to glass, which remains after metal has been obtained from rock

II. slag 2 BrE AmE verb ( past tense and past participle slagged , present participle slagging )

slag somebody ↔ off phrasal verb British English informal

to criticize someone in an unpleasant way, especially when this is unfair:

He’s always slagging her off behind her back.

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.