Meaning of “slap sth on” - Learner’s Dictionary

slap sth on

phrasal verb with slap us uk /slæp/ verb [ T ] present participle slapping, past tense and past participle slapped

to quickly put or spread something on a surface:

I'll just slap some make-up on.

(Definition of “slap sth on” from the Cambridge Learner’s Dictionary © Cambridge University Press)