Second year in pub about to become harmonious (2,4)
I believe the answer is:
in sync
'harmonious' is the definition.
(I've seen this in another clue)
'second year in pub about' is the wordplay.
'second year' becomes 'sy' (this could be a standard abbreviation of which I'm unaware).
'in' is an insertion indicator.
'pub' becomes 'inn' (an inn is a type of pub).
'about' becomes 'c' (circa).
'sy' put within 'inn' is 'insyn'.
'insyn'+'c'='IN SYNC'
'to become' acts as a link.
Can you help me to learn more?
(Other definitions for in sync that I've seen before include "Running together correctly" , "Harmonious" , "working well together" .)