Pieces match, but not on paper (8)
I believe the answer is:
mentally
'pieces match but not on paper' is the definition.
I can't judge whether this defines the answer.
'pieces match' is the wordplay.
'pieces' becomes 'men' (e.g. in chess).
'match' becomes 'tally' (synonyms).
'men'+'tally'='MENTALLY'
Can you help me to learn more?
(Other definitions for mentally that I've seen before include "Using the mind" , "how intelligence is developed" , "not physically" , "Intellectually" , "in the head" .)