Poets start drinking in pubs (5)
I believe the answer is:
bards
'poets' is the definition.
(bard is a kind of poet)
'start drinking in pubs' is the wordplay.
'start' 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 'drinking' is 'd'.
'd' going into 'bars' is 'BARDS'.
(Other definitions for bards that I've seen before include "Celtic minstrels or poets" , "Welsh poets" .)