stiff vs dead body

stiff and dead body both are nouns.

Word	Noun	Adjective	Verb	Adverb
stiff	Yes	Yes	No	Yes
dead body	Yes	No	No	No

As nouns, dead body is a hypernym of stiff; that is, dead body is a word with a broader meaning than stiff:

Other hypernyms of stiff include body.

stiff (noun)	dead body (noun)
the dead body of a human being	a natural object consisting of a dead animal or person
an ordinary man

stiff (adjective)	dead body (adjective)
having a strong physiological or chemical effect
rigidly formal
not moving or operating freely
very drunk
marked by firm determination or resolution; not shakable
strong, vigorous
incapable of or resistant to bending

stiff (adverb)	dead body (adverb)
in a stiff manner
to a great degree