boat vs kayak

boat and kayak both are nouns.

Word	Noun	Adjective	Verb	Adverb
boat	Yes	No	Yes	No
kayak	Yes	No	Yes	No

As verbs, kayak is a hyponym of boat; that is, kayak is a word with a more specific, narrower meaning than boat:

Other hyponyms of boat include motorboat, yacht, sail, row, canoe, paddle.

boat (noun)	kayak (noun)
a small vessel for travel on water	a small canoe consisting of a light frame made watertight with animal skins; used by Eskimos
a dish (often boat-shaped) for serving gravy or sauce

boat (verb)	kayak (verb)
ride in a boat on water	travel in a small canoe