Senior member's desire to act (5)
I believe the answer is:
doyen
'senior member's' is the definition.
(a senior or respected figure)
'desire to act' is the wordplay.
'desire' becomes 'yen' (yen can mean a longing or desire).
'to' means one lot of letters go next to another (I've seen this in other clues).
'act' becomes 'do' (to do is to act or execute a task).
'yen' put after 'do' is 'DOYEN'.
(Other definitions for doyen that I've seen before include "Most valued prof, eg" , "Prominent person in a particular field" , "As senior statesman" , "Senior male member of a group" , "Most prominent expert" .)