Brief way to classify rum (7)
I believe the answer is:
strange
'rum' is the definition.
(similar in meaning)
'brief way to classify' is the wordplay.
'brief way' becomes 'st' (abbreviation for street; 'brief' suggests an abbreviation).
'to classify' becomes 'range' (range can mean to rank or classify).
'st'+'range'='STRANGE'
(Other definitions for strange that I've seen before include "Odd kind of garnets" , "Unusual, surprising" , "Different" , "Surreal" , "Odd, alien" .)