He may be grand at chess (6)
I believe the answer is:
master
'he may' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'grand at chess' is the wordplay.
I cannot quite see how this works, but
'grand' could be 'm' (synonyms) and 'm' is located in the answer.
The remaining letters 'aster' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'be' acts as a link.
Can you help me to learn more?
(Other definitions for master that I've seen before include "'Jack of all trades and . . . . . . of none'" , "Main; overcome; original recording" , "Male teacher or ship's captain" , "Dominate" , "Artist of consummate skill" .)