A layer of silicon in a storehouse (7)
I believe the answer is:
deposit
'a layer' is the definition.
(I've seen this before)
'silicon in a storehouse' is the wordplay.
'silicon' becomes 'Si' (Si is the chemical symbol for silicon).
'in' indicates putting letters inside.
'a storehouse' becomes 'depot' (synonyms).
'si' inserted within 'depot' is 'DEPOSIT'.
'of' acts as a link.
(Other definitions for deposit that I've seen before include "Sum of money paid into a bank account" , "Lodge money in bank account" , "Money given as security" , "(Money or mineral) put down" , "Topside (anag) - put down" .)