Wood from area below raised flag (5)
I believe the answer is:
balsa
'wood' is the definition.
(type of wood)
'area below raised flag' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'below' means one lot of letters go next to another (in a down clue, some letters go below others).
'raised' says the letters should be written backwards (going up in a down clue).
'flag' becomes 'slab' (flag can mean a stone slab).
'slab' reversed gives 'bals'.
'a' put after 'bals' is 'BALSA'.
'from' acts as a link.
(Other definitions for balsa that I've seen before include "Strong, light wood" , "wood for raft" , "Raft-making S American corkwood" , "lightweight boat-builder" , "Lightweight timber" .)