supply vs slip in

supply is a noun but slip in is not a noun.

Word	Noun	Adjective	Verb	Adverb
supply	Yes	No	Yes	No
slip in	No	No	Yes	No

As verbs, slip in is a hyponym of supply; that is, slip in is a word with a more specific, narrower meaning than supply:

Other hyponyms of supply include insert, sneak in, stick in, toss in.

supply (noun)	slip in (noun)
the activity of supplying or providing something
offering goods and services for sale
an amount of something available for use

supply (verb)	slip in (verb)
state or say further	insert casually
give what is desired or needed, especially support, food or sustenance
give something useful or necessary to
circulate or distribute or equip with