To pull or draw someone under the surface of some body of liquid, especially due to the force of a current or low water pressure. A noun or pronoun can be used between "suck" and "under." The tides on these shores have sucked under far too many people, so we don't allow swimming here at all anymore. Contrary to pop culture and popular belief, it is extremely unlikely that quicksand will suck you under to your death. Though he was a very capable swimmer, the waves kept sucking him under and he drowned.