Take care of diet in a satisfactory way (8)
I believe the answer is:
farewell
'take' is the definition.
(thesaurus)
'care of diet in a satisfactory way' is the wordplay.
I cannot quite understand how this works, but
'diet' could be 'fare' (I've seen this in another clue) and 'fare' is located in the answer.
'satisfactory' could be 'well' (similar in meaning) and 'well' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for farewell that I've seen before include "It may be said when 15" , "Parting word" , "All the best" , "Wish on leave-taking" , "Goodbye, hope you get on" .)