underframe vs chassis

underframe and chassis both are nouns.

Word	Noun	Adjective	Verb	Adverb
underframe	Yes	No	No	No
chassis	Yes	No	No	No

As nouns, chassis is a hyponym of underframe; that is, chassis is a word with a more specific, narrower meaning than underframe:

underframe: the internal supporting structure that gives an artifact its shape
chassis: the skeleton of a motor vehicle consisting of a steel frame supported on springs that holds the body and motor

Other hyponyms of underframe include hoop.

underframe (noun)	chassis (noun)
the internal supporting structure that gives an artifact its shape	the skeleton of a motor vehicle consisting of a steel frame supported on springs that holds the body and motor
	a metal mounting for the circuit components of an electronic device
	alternative names for the body of a human being