Garment that is used after the end of August (3)
I believe the answer is:
tie
'garment' is the definition.
(tie is a kind of garment)
'that is used after the end of august' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'used after' means one lot of letters go next to another.
'the end of' suggests the final letters.
The final letter of 'august' is 't'.
'ie' put after 't' is 'TIE'.
(Other definitions for tie that I've seen before include "'Fasten, with string say (3)'" , "Draw for neckware" , "Failure to win" , "Bond > girl wearing this? Unlikely" , "Fasten, link to" .)