A block needs turning in light wood (5)

I believe the answer is:

balsa

I'm a little stuck... Click here to teach me more about this clue!

'light wood' is the definition.
(balsa is a light wood used in construction)

I can't explain the rest of the clue.

(Other definitions for balsa that I've seen before include "Very light timber" , "Raft-making S American corkwood" , "wood for raft" , "Tropical American tree" , "light raft" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app