Resin supplied by servant releasing key (3)
I believe the answer is:
lac
'resin' is the definition.
(resin secreted by lac insects)
'servant releasing key' is the wordplay.
'servant' becomes 'lackey' (a lackey is a servant or assistant).
'releasing' indicates named letters should be taken away.
'lackey' with 'key' taken away is 'LAC'.
'supplied by' is the link.
(Other definitions for lac that I've seen before include "Resinous material" , "Red resin secreted by insects" , "Natural product" , "thousands from India" , "Dark red resin - "Hotel du ___" (Anita Brookner)" .)