Fit for the task
I believe the answer is:
'fit for the task' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for able that I've seen before include "- -bodied; - seaman" , "Having the skills and qualifications required" , "Competent, capable" , "Gifted" , "... was I ere I saw Elba (palindrome)" .)