Feel OK, when nothing is fine (5)
I believe the answer is:
think
'feel' is the definition.
(thesaurus)
'ok when nothing is fine' is the wordplay.
I cannot really see how this works, but
'fine' could be 'thin' (similar in meaning) and 'thin' is present in the answer.
A single letter 'k' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for think that I've seen before include "Imagine" , "figure" , "Judge, consider" , "Cogitate; deem" , "Believe" .)