apply vs slap on

apply and slap on both are verbs.

Word	Noun	Adjective	Verb	Adverb
apply	No	No	Yes	No
slap on	No	No	Yes	No

As verbs, slap on is a hyponym of apply; that is, slap on is a word with a more specific, narrower meaning than apply:

Other hyponyms of apply include dab, swab, swob, daub, gum, dress, cream, cold-cream, putty, sponge on, clap on, slam on.

apply (verb)	slap on (verb)
ask (for something)	apply carelessly
refer (a word or name) to a person or thing
put into service; make work or employ for a particular purpose or for its inherent or natural purpose
coat, cover or smear a surface with
give or convey physically
avail oneself to
ensure observance of laws and rules
apply oneself to
be pertinent or relevant or applicable
be applicable to; as to an analysis