Ability to do a thankless task when unwell (5)
I believe the answer is:
skill
'ability' is the definition.
(I know that ability can be written as skill)
'do a thankless task when unwell' is the wordplay.
I cannot really understand how this works, but
'unwell' could be 'ill' (similar in meaning) and 'ill' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for skill that I've seen before include "Expertise, dexterity" , "Ability acquired by training" , "Craft; dexterity" , "Talent" , "Prowess" .)