Herb in sink close to spice (4)
I believe the answer is:
sage
'herb' is the definition.
(I know that sage is a type of herb)
'sink close to spice' is the wordplay.
'sink' becomes 'sag' (sagging is a kind of sinking).
'close to' suggests the final letters (the close/ending of).
The final letter of 'spice' is 'e'.
'sag'+'e'='SAGE'
'in' is the link.
(Other definitions for sage that I've seen before include "Solon, for instance" , "___ and onion" , "Clever" , "Learned" , "Herb for the wise one" .)