storage space vs cellar

storage space and cellar both are nouns.

Word	Noun	Adjective	Verb	Adverb
storage space	Yes	No	No	No
cellar	Yes	No	No	No

As nouns, cellar is a hyponym of storage space; that is, cellar is a word with a more specific, narrower meaning than storage space:

Other hyponyms of storage space include cache, wine cellar, closet, cupboard, drawer, root cellar, stacks.

storage space (noun)	cellar (noun)
the area in any structure that provides space for storage	the lowermost portion of a structure partly or wholly below ground level; often used for storage
	storage space where wines are stored
	an excavation where root vegetables are stored