Entry 1 sense Webster, 1913 Undertone /ŭn'-dẽrt-ōnˌ/ · Un·der·tone · IPA /ˈʌndə(ɹ)təʊn/ 01 n. A low or subdued tone or utterance; a tone less loud than usual. 1. A low or subdued tone or utterance; a tone less loud than usual.