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," from PIE root *ten- "to stretch." 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.

"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.