tone: [14] English acquired tone via Old French ton and Latin tonus from Greek tónos ‘stretching, tension’, hence ‘sound’. This in turn went back to the Indo-European base *ton-, *ten- ‘stretch’, which also produced English tend, tense, thin, etc. The semantic transference from ‘tension’ to ‘sound’ may have arisen from the notion of tightening the strings of a musical instrument, but it could also be due to association with another Indo-European base *ton-, meaning ‘resound’ (source of English thunder). The derivative tonic [17] comes ultimately from Greek tonikós. Tune is an unexplained variant of tone. => tend, tense, tenuous, thin, tune
tone (n.)
mid-14c., "musical sound or note," from Old French ton "musical sound, speech, words" (13c.) and directly from Latin tonus "a sound, tone, accent," literally "stretching" (in Medieval Latin, a term peculiar to music), from Greek tonos "vocal pitch, raising of voice, accent, key in music," originally "a stretching, tightening, taut string," related to teinein "to stretch" (see tenet). Sense of "manner of speaking" is from c. 1600. First reference to firmness of body is from 1660s. As "prevailing state of manners" from 1735; as "style in speaking or writing which reveals attitude" from 1765. Tone-deaf is from 1880; tone-poem from 1845.
tone (v.)
"to impart tone to," 1811, from tone (n.). Related: Toned; toning. To tone (something) down originally was in painting (1831); general sense of "reduce, moderate" is by 1847.