A touch of numbness on tongue, diminishing a flavour (8)
I believe the answer is:
angelica
'tongue diminishing a flavour' is the definition.
I can't tell whether this defines the answer.
'a touch of numbness on' is the wordplay.
'touch of numbness' becomes 'angelic' (I am not sure about this - if you are sure you should believe this answer much more).
'on' says to put letters next to each other.
'a' after 'angelic' is 'ANGELICA'.
Can you help me to learn more?
(Other definitions for angelica that I've seen before include "Nag Alice to get fragrant plant" , "Candied stem, decorates cake" , "may be sitting on top of the trifle" , "Candied part of herbs - nag Alice (anag)" , "Candied plant stalks" .)