raft vs balsa raft

raft and balsa raft both are nouns.

Word	Noun	Adjective	Verb	Adverb
raft	Yes	No	Yes	No
balsa raft	Yes	No	No	No

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

raft: a flat float (usually made of logs or planks) that can be used for transport or as a platform for swimmers
balsa raft: a light raft made of balsa

Other hyponyms of raft include Kon Tiki, Carling float, life raft.

raft (noun)	balsa raft (noun)
a flat float (usually made of logs or planks) that can be used for transport or as a platform for swimmers	a light raft made of balsa
a foundation (usually on soft ground) consisting of an extended layer of reinforced concrete
(often followed by `of') a large number or amount or extent