gimmick vs fast one

gimmick and fast one both are nouns.

Word	Noun	Adjective	Verb	Adverb
gimmick	Yes	No	No	No
fast one	Yes	No	No	No

As nouns, fast one is a hyponym of gimmick; that is, fast one is a word with a more specific, narrower meaning than gimmick:

Other hyponyms of gimmick include mnemonic, trick.

gimmick (noun)	fast one (noun)
any clever maneuver	a cunning or deceitful action or device
something unspecified whose name is either forgotten or not known
a drawback or difficulty that is not readily evident