Deserts peer, abandoning king (3)
I believe the answer is:
due
'deserts' is the definition.
(what someone deserves)
'peer abandoning king' is the wordplay.
'peer' becomes 'duke' (type of peer).
'abandoning' indicates named letters should be taken away.
'king' becomes 'K' (abbreviation for king in chess).
'duke' with 'k' removed is 'DUE'.
(Other definitions for due that I've seen before include "Expected; appropriate" , "deserts" , "Deserved or unpaid" , "Required; proper" , "Appropriate - fee - now owing" .)