barge vs pontoon

barge and pontoon both are nouns.

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

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

barge: 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 barge include dredger, houseboat, scow, Norfolk wherry, wherry.

barge (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

barge (verb)	pontoon (verb)
push one's way
transport by barge on a body of water