An accumulation of silicon in a storehouse (7)
I believe the answer is:
deposit
'an accumulation' is the definition.
(I know that deposit is a type of accumulation)
'silicon in a storehouse' is the wordplay.
'silicon' becomes 'Si' (chemical symbol).
'in' indicates putting letters inside.
'a storehouse' becomes 'depot' ('depot' can be a synonym of 'storehouse').
'si' going into 'depot' is 'DEPOSIT'.
'of' is the link.
(Other definitions for deposit that I've seen before include "fur, possibly" , "Topside (anag) - put down" , "Precipitate" , "Money up front" , "Drop" .)