Moves slowly in game that's not finished (6)
I believe the answer is:
'moves slowly' is the definition.
(I've seen this before)
'in game that's not finished' is the wordplay.
'game' becomes 'chess' (chess is a kind of game).
'that's not finished' means to remove the last letter.
'chess' with its final letter taken away is 'ches'.
(Other definitions for inches that I've seen before include "Niches (anag.)" , "Edges slowly" , "Twelves of these in a foot" , "Short lengths" , "Moves slowly and cautiously" .)