Rob of a vessel? (3)
I believe the answer is:
mug
I believe this is a double definition.
'rob' is the first definition.
(slang)
'a vessel?' is the second definition.
(mug is a kind of vessel)
'of' acts as a link.
(Other definitions for mug that I've seen before include "Charlie" , "Gullible person" , "Drinking vessel, by gum" , "Slangy victim, by gum" , "Beaker" .)