Short expression wears thin in speech (6)
I believe the answer is:
phrase
'short expression' is the definition.
(I've seen this before)
'wears thin in speech' is the wordplay.
'wears thin' becomes 'frays'.
'in speech' indicates a 'sounds like' (homophone) clue.
'frays' sounds like 'PHRASE'.
(Other definitions for phrase that I've seen before include "Group of words forming part of a sentence" , "a certain expression" , "Put into words" , "Present" , "Sentence unit" .)