Entry 1 sense Webster, 1913 Undertow /ŭn'-dẽrt-ōˌ/ · Un·der·tow · IPA /ˈʌndərtˌoʊ/ 01 n. The current that sets seaward near the bottom when waves are breaking upon the shore. 1. The current that sets seaward near the bottom when waves are breaking upon the shore.(Naut.)