the current that is below the surface that sets seaward or along the beach when waves are breaking upon the shore and that moves away from the shore;
e.g. They incorrectly assumed he was swept away by the undertow while swimming.
(noun)
an implicit quality, feeling, or influence, underlying the surface aspects of something and that runs contrary to one's normal feeling and leaves a distinct impression;
e.g. Beneath the feelings of nostalgia, there is an undertow of grief for lost youth.