Sage or coriander originally in brew (6)
I believe the answer is:
oracle
'sage' is the definition.
(I've seen this before)
'or coriander originally in brew' is the wordplay.
'originally' suggests taking the first letters.
'in' indicates putting letters inside.
'brew' becomes 'ale' (ale is a kind of brew).
The initial letter of 'coriander' is 'c'.
'c' inserted within 'ale' is 'acle'.
'or'+'acle'='ORACLE'
(Other definitions for oracle that I've seen before include "Adviser t" , "Source of divine advice" , "Place where ancient Greeks consulted gods, as at Delphi" , "Shrine; its message" , "Medium for prophecy" .)