Black-marketeer sending big guns over (4)
I believe the answer is:
spiv
'black-marketeer' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for spiv that I've seen before include "Agreement" , "He's a flashy dresser who sells dodgy goods" , "Flashy crook" , "Flashily dressed dodgy dealer" , "Non-kosher supplier" .)