Poets start to drink in pubs (5)
I believe the answer is:
bards
'poets' is the definition.
(bard is a kind of poet)
'start to drink in pubs' is the wordplay.
'start to' says to take the initial letters.
'in' means one lot of letters goes inside another.
'pubs' becomes 'bars' (a bar is a pub).
The first letter of 'drink' is 'd'.
'd' placed within 'bars' is 'BARDS'.
(Other definitions for bards that I've seen before include "Welsh poets" , "Celtic minstrels or poets" .)