overtone n.

word-forming element meaning variously "above; highest; across; higher in power or authority; too much; above normal; outer; beyond in time, too long," from Old English ofer (from PIE root *uper "over"). Over and its Germanic relations were widely used as prefixes, and sometimes could be used with negative force. This is rare in Modern English, but compare Gothic ufarmunnon "to forget," ufar-swaran "to swear falsely;" Old English ofercræft "fraud."

In some of its uses, moreover, over is a movable element, which can be prefixed at will to almost any verb or adjective of suitable sense, as freely as an adjective can be placed before a substantive or an adverb before an adjective. [OED]

Among the old words not now existing are Old English oferlufu (Middle English oferlufe), literally "over-love," hence "excessive or immoderate love." Over- in Middle English also could carry a sense of "too little, below normal," as in over-lyght "of too little weight" (c. 1400), overlitel "too small" (mid-14c.), oversmall (mid-13c.), overshort, etc.

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," which is related to teinein "to stretch" (from PIE root *ten- "to stretch").

The sense of "manner of speaking" is from c. 1600. In reference to firmness of body, from 1660s. As "prevailing state of manners" from 1735; as "style in speaking or writing which reveals attitude" from 1765. Tone-deaf is by 1880; tone-poem by 1845.