hoy vs pontoon

hoy and pontoon both are nouns.

Word	Noun	Adjective	Verb	Adverb
hoy	Yes	No	No	No
pontoon	Yes	No	No	No

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

hoy: a flatbottom boat for carrying heavy loads (especially on canals)
pontoon: (nautical) a floating structure (as a flat-bottomed boat) that serves as a dock or to support a bridge

Other hyponyms of hoy include dredger, houseboat, scow, Norfolk wherry, wherry.

hoy (noun)	pontoon (noun)
a flatbottom boat for carrying heavy loads (especially on canals)	a float supporting a seaplane
	(nautical) a floating structure (as a flat-bottomed boat) that serves as a dock or to support a bridge