Pure friend at sea taking in end of cruise (7)
I believe the answer is:
refined
'pure' is the definition.
('refined' can be similar in meaning to 'pure')
'friend at sea taking in end of cruise' is the wordplay.
'at sea' indicates anagramming the letters.
'taking in' means one lot of letters goes inside another.
'end of' indicates one should take the final letters.
The final letter of 'cruise' is 'e'.
'friend' anagrammed gives 'rfined'.
'rfined' going around 'e' is 'REFINED'.
(Other definitions for refined that I've seen before include "Discerning" , "Elegant, cultured" , "Free from vulgarity" , "Polished" , "Tasteful; genteel" .)