Join band, briefly (3)
I believe the answer is:
tie
'join' is the definition.
(tie can mean to connect or join together)
'band briefly' is the wordplay.
'band' becomes 'tier' (I've seen this before).
'briefly' means to remove the last letter.
'tier' with its final letter removed is 'TIE'.
(Other definitions for tie that I've seen before include "Affiliation" , "Encumbrance" , "Restrict; link" , "Knot; limit" , "Secure (with string)" .)