skeleton vs skeleton in the cupboard

skeleton and skeleton in the cupboard both are nouns.

Word	Noun	Adjective	Verb	Adverb
skeleton	Yes	No	No	No
skeleton in the cupboard	Yes	No	No	No

As nouns, skeleton and skeleton in the cupboard are synonyms defined as:

Other synonyms of skeleton include skeleton in the closet.

skeleton (noun)	skeleton in the cupboard (noun)
the internal supporting structure that gives an artifact its shape	a scandal that is kept secret
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