Less than the right amount for a hat (3)
I believe the answer is:
tam
'a hat' is the definition.
(thesaurus)
'less than the right amount for' is the wordplay.
'less than' means to remove the last letter (not the full word).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'right' becomes 'ar' (I've seen this in other clues).
'amount for' becomes 'm' (I can't explain this - if you can you should believe this answer much more).
't'+'ar'='tar'
'tar' with its final letter removed is 'ta'.
'ta'+'m'='TAM'
Can you help me to learn more?
(Other definitions for tam that I've seen before include "TV audience ratings" , "Turn over the mat for a cap" , "Scotsman's cap" , "'Scottish cloth cap, in short (3)'" , "These ratings measure TV audiences" .)