Open top of bottle, European drink (5)
I believe the answer is:
begin
'open' is the definition.
(thesaurus)
'top of bottle european drink' is the wordplay.
'top of' suggests taking the first letters.
'drink' becomes 'gin' (gin is a kind of drink).
The first letters of 'bottle european' is 'be'.
'be'+'gin'='BEGIN'
(Other definitions for begin that I've seen before include "former Israeli Nobel peace prize winner" , "Partly open" , "Clandestine, furtive" , "Get cracking" , "Make a start" .)