drop dead vs stifle

drop dead is not a noun while stifle is a noun.

Word	Noun	Adjective	Verb	Adverb
drop dead	No	No	Yes	No
stifle	Yes	No	Yes	No

As verbs, stifle is a hyponym of drop dead; that is, stifle is a word with a more specific, narrower meaning than drop dead:

drop dead: pass from physical life and lose all bodily attributes and functions necessary to sustain life
stifle: be asphyxiated; die from lack of oxygen

Other hyponyms of drop dead include abort, asphyxiate, suffocate, buy it, pip out, drown, predecease, famish, starve, fall, succumb, yield.

drop dead (noun)	stifle (noun)
	joint between the femur and tibia in a quadruped; corresponds to the human knee

drop dead (verb)	stifle (verb)
pass from physical life and lose all bodily attributes and functions necessary to sustain life	suppress or constrain so as to lessen in intensity
	be asphyxiated; die from lack of oxygen
	suppress in order to conceal or hide
	impair the respiration of or obstruct the air passage of