slim down vs thin

slim down is not an adjective while thin is an adjective.

Word	Noun	Adjective	Verb	Adverb
slim down	No	No	Yes	No
thin	No	Yes	Yes	Yes

As verbs, slim down and thin are synonyms defined as:

Other synonyms of slim down include melt off, reduce, slenderize, slim.

slim down (adjective)	thin (adjective)
	of relatively small extent from one surface to the opposite or in cross section
	relatively thin in consistency or low in density; not viscous
	lacking excess flesh
	(of sound) lacking resonance or volume
	not dense
	very narrow
	lacking spirit or sincere effort
	lacking substance or significance

slim down (verb)	thin (verb)
take off weight	take off weight
	lose thickness; become thin or thinner
	make thin or thinner
	lessen the strength or flavor of a solution or mixture

slim down (adverb)	thin (adverb)
	without viscosity