First of all, bottle emptied, removing extremely tight cap (5)
I believe the answer is:
beret
'cap' is the definition.
(I know that beret is a type of cap)
'first of all bottle emptied removing extremely tight' is the wordplay.
'first of all' says to take the initial letters.
The initial letters of 'bottle emptied removing extremely tight' is 'BERET'.
(Other definitions for beret that I've seen before include "Soft brimless cap" , "Felt hat" , "Soft peak-less kind of cap" , "French style cap" , "Soft flat hat" .)