Wood resin running short (5)
I believe the answer is:
balsa
'wood' is the definition.
(balsa is a kind of wood)
'resin running short' is the wordplay.
'resin' becomes 'balsam' (balsam is a kind of resin).
'running short' means to remove the last letter.
'balsam' with its final letter taken off is 'BALSA'.
(Other definitions for balsa that I've seen before include "Wood used in model making" , "wood for raft" , "Wood used by model makers" , "Very light timber" , "Tree with light soft wood" .)