smell vs get a whiff

smell is a noun but get a whiff is not a noun.

Word	Noun	Adjective	Verb	Adverb
smell	Yes	No	Yes	No
get a whiff	No	No	Yes	No

As verbs, get a whiff is a hyponym of smell; that is, get a whiff is a word with a more specific, narrower meaning than smell:

Other hyponyms of smell include sniff, whiff, nose, scent, wind, snuff, snuffle, get a noseful.

smell (noun)	get a whiff (noun)
the act of perceiving the odor of something
any property detected by the olfactory system
the faculty that enables us to distinguish scents
the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form
the general atmosphere of a place or situation and the effect that it has on people

smell (verb)	get a whiff (verb)
become aware of not through the senses but instinctively	smell strongly and intensely
emit an odor
inhale the odor of; perceive by the olfactory sense
smell bad
have an element suggestive (of something)