Wood shot away from army base (5)

I believe the answer is:

alder

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

'wood' is the definition.
(I know that alder is a type of wood)

I can't explain the remainder of the clue.

(Other definitions for alder that I've seen before include "Tree with catkins" , "Catkin-bearing tree" , "Shrub or tree with cone-like fruits" , "Tree or shrub whose wood is resistant to underwater rot" , "Forward movement" .)

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