Talk about small herb (7)
I believe the answer is:
parsley
'herb' is the definition.
(I know that parsley is a type of herb)
'talk about small' is the wordplay.
'talk' becomes 'parley' (to parley is to talk with an enemy).
'about' is an insertion indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'parley' going around 's' is 'PARSLEY'.
(Other definitions for parsley that I've seen before include "Herb with either flat or crinkly leaves" , "Cow -, fool's - and stone - are all plants" , "You might misuse this herb sparely" , "Aromatic herb with flat or crinkly leaves" , "Herb for garnishing" .)