Socialise together (6)
I believe the answer is:
hobnob
'socialise together' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hobnob that I've seen before include "Socialise informally" , "Spend friendly time together" , "Spend time together, socialise" , "Socialize, rub elbows with" , "mix informally" .)