Bind or untie, possibly (5)
I believe the answer is:
unite
'bind' is the definition.
The answer and definition can be both to do with social activities as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
'untie possibly' is the wordplay.
'possibly' is an anagram indicator.
'untie' anagrammed gives 'UNITE'.
'or' is the link.
Can you help me to learn more?
(Other definitions for unite that I've seen before include "Link" , "Club together" , "Get together" , "Join together, merge" , "ally" .)