small boat vs skiff

small boat and skiff both are nouns.

Word	Noun	Adjective	Verb	Adverb
small boat	Yes	No	No	No
skiff	Yes	No	No	No

As nouns, skiff is a hyponym of small boat; that is, skiff is a word with a more specific, narrower meaning than small boat:

small boat: a boat that is small
skiff: any of various small boats propelled by oars or by sails or by a motor

Other hyponyms of small boat include canoe, cockleshell, coracle, dinghy, dory, rowboat, gig, racing boat, yawl.

small boat (noun)	skiff (noun)
a boat that is small	any of various small boats propelled by oars or by sails or by a motor