Almost everyone swallowing drop of rum (that is, a spirit) (5)
I believe the answer is:
ariel
'a spirit' is the definition.
(I've seen this before)
'almost everyone swallowing drop of rum that is' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'everyone' becomes 'all' (I've seen this before).
'swallowing' is an insertion indicator.
'drop of' indicates taking the first letters.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
The first letter of 'rum' is 'r'.
'all' with its last letter taken away is 'al'.
'r'+'ie'='rie'
'al' enclosing 'rie' is 'ARIEL'.
(Other definitions for ariel that I've seen before include "Fairy in "The Tempest"" , "Shakespearean role" , "Moulding round top of wall" , "Character pined once, unable to escape" , "Sycorax victim (Tempest)" .)