skeleton vs underframe

skeleton and underframe both are nouns.

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

As nouns, skeleton and underframe are synonyms defined as:

skeleton and underframe: the internal supporting structure that gives an artifact its shape

Other synonyms of skeleton include frame, skeletal frame.

skeleton (noun)	underframe (noun)
the internal supporting structure that gives an artifact its shape	the internal supporting structure that gives an artifact its shape
the hard structure (bones and cartilages) that provides a frame for the body of an animal
a scandal that is kept secret
something reduced to its minimal form