Clipped manner of speaking ultimately felt stupid (5)
I believe the answer is:
idiot
'stupid' is the definition.
(thesaurus)
'clipped manner of speaking ultimately felt' is the wordplay.
'clipped' means to remove the last letter.
'manner of speaking' becomes 'idiom' (I've seen this before).
'ultimately felt' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'idiom' with its last letter taken off is 'idio'.
'idio'+'t'='IDIOT'
Can you help me to learn more?
(Other definitions for idiot that I've seen before include "nutter" , "Dope" , "Dostoevsky hero" , "Sap" , "Fool, silly person" .)