Second dram - a bargain (4)
I believe the answer is:
snip
'a bargain' is the definition.
(slang term for a good deal)
'second dram' is the wordplay.
'second' becomes 's' (common abbreviation).
'dram' becomes 'nip' (I've seen this before).
's'+'nip'='SNIP'
(Other definitions for snip that I've seen before include "Steal" , "Cut with shears" , "Easy to do - use pins" , "Cut - certainty" , "Bargain (informal)" .)