Spindle left in fire (4)
I believe the answer is:
axle
'spindle' is the definition.
(I've seen this in another clue)
'left in fire' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'fire' becomes 'axe' (I've seen this in other clues).
'l' going into 'axe' is 'AXLE'.
(Other definitions for axle that I've seen before include "Bar on which wheel revolves" , "Rod attachment to wheels" , "Spindle between wheels" , "Wheel-shaft" , "Wheel pivot" .)