Meaning of “slip out” - Learner’s Dictionary

slip out

phrasal verb with slip us uk /slɪp/ verb present participle slipping, past tense and past participle slipped

If a remark slips out, you say it without intending to:

I didn't mean to tell anyone you were getting married - it just slipped out.

(Definition of “slip out” from the Cambridge Learner’s Dictionary © Cambridge University Press)