Mother, it seems, is a winner at chess (5)
I believe the answer is:
mater
'mother' is the definition.
(old-fashioned term for mother)
'it seems is a winner at chess' is the wordplay.
I cannot quite understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'a' is within the answer.
The remaining letters 'mer' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mater that I've seen before include "having children" , "Mother (sl.)" , "mum's the word" , "The alma . . . . . Is the old school (5)" , "One marrying" .)