Plant secretion extremely rare? Wrong (5)
I believe the answer is:
resin
'plant secretion' is the definition.
'extremely rare? wrong' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'wrong' becomes 'sin' (I've seen this before).
'rare' with its centre removed is 're'.
're'+'sin'='RESIN'
(Other definitions for resin that I've seen before include "Substance produced from sap of some plants and trees" , "Synthetic substance" , "plastic material" , "Sticky stuff from pine trees" , "Viscous substance in some trees" .)