Mother is one who wins a game of chess (5)
I believe the answer is:
mater
This could be a double definition.
'mother' is the first definition.
(old-fashioned term for mother)
'one who wins a game of chess' is the second definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'is' is the link.
Can you help me to learn more?
(Other definitions for mater that I've seen before include "mum's the word" , "parent" , "See 12" , "Mother (Latin or old slang)" , "Dam" .)