VASO = vessel
+
PRESSIN = pressing
Separate vasopressin into VASO (sounds like vessel) and PRESSIN (sounds like pressing). Now imagine a hand pressing (PRESSIN) on a blood vessel (VASO), reminding you of vasoconstriction. At the same time, imagine a hand pressing (PRESSIN) on the collecting duct, stopping water flow, like how vasopressin stops water from leaving the body via urine.

V1 & V2 agonist
VASO = vessel | PRESSIN = pressing