From Longman Dictionary of Contemporary Englishslap something ↔ on phrasal verb informal1 PUTto put or spread something quickly or carelessly onto a surface She ran upstairs and slapped on some make-up.slap something on something We could slap some paint on it.2 ADDto suddenly announce a new charge, tax etc or say that something is not allowed – used especially when you think this is unfair Many tour operators slap on supplements for single people.slap something on something In 1977, the president slapped a ban on the commercial reprocessing of nuclear fuel. → slap→ See Verb table
