Herb for a wise man (4)
I believe the answer is:
sage
I believe this clue is a double definition.
'herb' is the first definition.
(sage is a kind of herb)
'wise man' is the second definition.
(sage is a kind of wise man)
'for a' is the link.
(Other definitions for sage that I've seen before include "Profoundly wise" , "cheesemongers associate with Derby" , "Clever" , "Wise man - flavoursome plant" , "Learned" .)