He is used to having high scores (4)
I believe the answer is:
alto
'he is used to having high scores' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he is used to' is the wordplay.
I cannot really understand how this works, but
'he' could be 'al' and 'al' is found in the answer.
'to' is within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for alto that I've seen before include "Second of four parts (in singing)" , "Counter-tenor or contralto" , "Highest male voice: lowest female voice" , "Singing range" , "Kind of singing voice, male or female" .)