Bit of firewood? (3)
I believe the answer is:
'bit of firewood?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
This is all the clue.
Can you help me to learn more?
(Other definitions for fir that I've seen before include "Conifer tree" , "Tree for an Irishman" , "Evergreen conifer" , "Pine tree for Gaelic men?" , "wood" .)