Definition - A unit of pitch change for a given language. English has about seven tones.
(1) In some languages tone allows speakers to distinguish between different words that are otherwise pronounced exactly the same way.
(2) Tone refers to the pitch-pattern within a word, whereas intonation refers to the pitch-pattern of a whole clause or sentence.

Example -
"In the Danish dialect spoken in Sundeved … two … tones are distinguished, one high and the other low.… These tones often serve to keep words … apart that would be perfect homonyms but for the accent."
(Jespersen Progress Lang. 86)

Etymology -
The word derives via Latin from the Greek tonos, vocal pitch or raising of voice (originally "a stretching, taut string").

Oxford English Dictionary -
The first citation for the word in this sense is from 1679:
"At Garways, Chinese Language Tones."
(R. Hooke Diary 14 May (1935), 412)

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