From Longman Dictionary of Contemporary Englishundertowun‧der‧tow /ˈʌndətəʊ $ -dərtoʊ/ noun [singular] 1 HEOthe water current under the surface of the sea, that pulls away from the land when a wave comes onto the shore The dangerous undertow means that swimming is not allowed.2 a tendency or feeling that seems weak, but in fact has a strong effectundertow of The humour of the novel cannot hide an undertow of sadness.
Examples from the Corpus
undertow• The wave had a great deal of undertow.• Sylvie had raved, raved with that undertow of intensity which always made her seem to be speaking the truth.• Regardless of the undertow of danger, Johnnie would not give back the diaphragm case.• But it's the undertow of precocious sexuality, the child-woman come-on, that's more worrying. 