Feeling unusually frail (5)
I believe the answer is:
flair
'feeling' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'unusually frail' is the wordplay.
'unusually' indicates anagramming the letters.
'frail' is an anagram of 'FLAIR'.
Can you help me to learn more?
(Other definitions for flair that I've seen before include "Natural ability or elegance" , "?lan, dash" , "Bent" , "Natural talent or panache" , "gift" .)