Check on spare glove (8)
I believe the answer is:
gauntlet
'glove' is the definition.
(gauntlet is a kind of glove)
'check on spare' is the wordplay.
'check' becomes 'let' (I've seen this in other clues).
'on' is a charade indicator (letters next to each other).
'spare' becomes 'gaunt' (both can mean thin).
'let' after 'gaunt' is 'GAUNTLET'.
(Other definitions for gauntlet that I've seen before include "Glove with long sleeve, thrown down challenge" , "Throw this glove down as a challenge" , "It may be thrown down or run" , "Long-sleeved glove" , "handy protection" .)