Join part of brass section in retirement (4)
I believe the answer is:
abut
'join' is the definition.
(I've seen this before)
'part of brass section in retirement' is the wordplay.
I cannot quite understand how this works, but
'part' could be 'ut' (ut is a kind of part) and 'ut' is found in the answer.
The remaining letters 'ab' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for abut that I've seen before include "Touch, lean on" , "Impinge" , "Adjoin, press up against" , "Adjoin, touch" , "Of building or land, end or lean against" .)