Spirit's almost undiluted drink (7)
I believe the answer is:
purport
'spirit's' is the definition.
('purport' can be a synonym of 'spirit')
'almost undiluted drink' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'undiluted' becomes 'pure' ('pure' can be a synonym of 'undiluted').
'drink' becomes 'port' (port is a kind of drink**).
'pure' with its final letter removed is 'pur'.
'pur'+'port'='PURPORT'
(Other definitions for purport that I've seen before include "Seem or claim (to be)" , "Spirit" , "Meaning, substance" , "Intended meaning" , "Pretend; meaning" .)