One thing we get together for (5)
I believe the answer is:
unity
'one' is the definition.
(synonyms)
'thing we get together for' is the wordplay.
I cannot really understand how this works, but
'thing' could be 'unit' (I have seen 'Single thing' mean 'unit' so perhaps 'thing' could also mean 'unit') and 'unit' is found within the answer.
A single letter 'y' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for unity that I've seen before include "State of togetherness" , "A single whole" , "Accord" , "Concord" , "Number one" .)