slap something ↔ on phrasal verb informal ( see also ↑ slap )
1 . to 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 . to 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.