Bargains in fantastic sales, opening from Thursday (6)
I believe the answer is:
steals
'bargains' is the definition.
('steal' can be a synonym of 'bargain')
'fantastic sales opening from thursday' is the wordplay.
'fantastic' is an anagram indicator.
'opening from' indicates taking the first letters.
The first letter of 'thursday' is 't'.
'sales'+'t'='salest'
'salest' with letters rearranged gives 'STEALS'.
'in' is the link.
(Other definitions for steals that I've seen before include "Purloins" , "Pilfers" , "Pilfer, filch" , "Takes without owner's consent" , "Takes property without right or permission" .)