Desires wild grouse, not duck (5)
I believe the answer is:
urges
'desires' is the definition.
Although both the answer and definition are verbs in their -s form, I don't understand how they can define each other.
'wild grouse not duck' is the wordplay.
'wild' is an anagram indicator.
'not' indicates named letters should be taken away.
'duck' becomes 'o'.
'grouse' with 'o' taken away is 'gruse'.
'gruse' is an anagram of 'URGES'.
Can you help me to learn more?
(Other definitions for urges that I've seen before include "Advocates strongly" , "Inner promptings" , "Presses to do something" , "Encourages" , "Persuades to do something" .)