hobby vs spelaeology

hobby and spelaeology both are nouns.

Word	Noun	Adjective	Verb	Adverb
hobby	Yes	No	No	No
spelaeology	Yes	No	No	No

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

Other hyponyms of hobby include speleology, pigeon keeping.

hobby (noun)	spelaeology (noun)
an auxiliary activity	the pastime of exploring caves
small Old World falcon formerly trained and flown at small birds	the scientific study of caves
a child's plaything consisting of an imitation horse mounted on rockers; the child straddles it and pretends to ride