spare-time activity vs hobby

spare-time activity and hobby both are nouns.

Word	Noun	Adjective	Verb	Adverb
spare-time activity	Yes	No	No	No
hobby	Yes	No	No	No

As nouns, spare-time activity and hobby are synonyms defined as:

Other synonyms of spare-time activity include avocation, by-line, pursuit, sideline.

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