Small nails – a lot (6)
I believe the answer is:
stacks
'a lot' is the definition.
(I've seen this before)
'small nails' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'nails' becomes 'tacks' (tack is a kind of nail).
's'+'tacks'='STACKS'
(Other definitions for stacks that I've seen before include "A lot (of hay?)" , "Orderly heaps as of hay" , "Orderly piles or heaps" , "Ricks" , "Tons" .)