To cover over completely, as by a great wave; to overflow and bury beneath; to ingulf; hence, figuratively, to immerse and bear down; to overpower; to crush; to bury; to oppress, etc
If a group of people overwhelm a place or another group, they gain complete control or victory over them. It was clear that one massive Allied offensive would overwhelm the weakened enemy. = overpower
If you are overwhelmed by a feeling or event, it affects you very strongly, and you do not know how to deal with it. He was overwhelmed by a longing for times past The need to talk to someone, anyone, overwhelmed her. = overpower + overwhelmed over·whelmed Sightseers may be a little overwhelmed by the crowds and noise