Balsa or balsa wood is a very light wood from a South American tree.
balsa in British English
(ˈbɔːlsə)
noun
1.
a bombacaceous tree, Ochroma lagopus, of tropical America
2. Also called: balsawood
the very light wood of this tree, used for making rafts, etc
3.
a light raft
Word origin
C18: from Spanish: raft
balsa in American English
(ˈbɔlsə)
US
noun
1.
any of several tropical American trees (genus Ochroma) of the bombax family that yield an extremely light and buoyant wood used for rafts, model airplanes, etc.
2.
the wood
3.
a raft, esp. one made up of a frame resting on cylindrical floats