slam dunk vs slam-dunk

slam dunk is a noun but slam-dunk is not a noun.

Word	Noun	Adjective	Verb	Adverb
slam dunk	Yes	No	No	No
slam-dunk	No	No	Yes	No

slam dunk (noun)	slam-dunk (noun)
a forceful dunk
something that is a sure to occur; a foregone conclusion

slam dunk (verb)	slam-dunk (verb)
	make a slam dunk; shoot a basketball in a slam dunk
	make a forceful move against