Shell of some identical seed (6)
I believe the answer is:
sesame
'seed' is the definition.
(sesame seed is a kind of seed)
'shell of some identical' is the wordplay.
'shell of' means to remove the middle letters.
'identical' becomes 'same' (similar in meaning).
'some' with its middle removed is 'se'.
'se'+'same'='SESAME'
(Other definitions for sesame that I've seen before include "Seed used in flavouring" , "Plant yielding seeds used for flavouring bread" , "Password of the Arabian Nights" , "A seed; a TV Street" , "Open .... is a pantomime cry" .)