If there is an undertow of a feeling, that feeling exists in such a weak form that you are hardly aware of it, but it influences the way you think or behave. an undertow of sadness. = undercurrent
(1) A current below water surface flowing seaward; the receding water below the surface from waves breaking on a shelving beach (2) Actually undertow is largely mythical As the BACKWASH of each wave flows down the beach, a current is formed which flows seaward However, it is a periodic phenomenon The most common phenomena expressed as undertow are actually rip currents
{i} strong current under the surface of the water; strong current under the surface of the water that is moving in a different direction than the surface current, countercurrent
the seaward undercurrent created after waves have broken on the shore an inclination contrary to the strongest or prevailing feeling; "his account had a poignant undertow of regret