Partner of ready and willing (4)
I believe the answer is:
able
'partner of ready and willing' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for able that I've seen before include "Capable seaman" , "Bright" , "Having the necessary capacity (to do something)" , "Talented" , "Competent as, say, sailor" .)