Mellow blend of tea and rum (6)
I believe the answer is:
mature
'mellow' is the definition.
('mature' can be similar in meaning to 'mellow')
'blend of tea and rum' is the wordplay.
'blend of' indicates anagramming the letters (I've seen this in other clues).
'and' means one lot of letters go next to another (I've seen this in other clues).
'tea' after 'rum' is 'rumtea'.
'rumtea' is an anagram of 'MATURE'.
(Other definitions for mature that I've seen before include "Fully developed physically" , "Old film star" , "Fully grown and adult" , "Ripen or grow up" , "Grow older" .)