to·​nus ˈtō-nəs How to pronounce tonus (audio)
: tone sense 9b
especially : a state of partial contraction characteristic of normal muscle

Examples of tonus in a Sentence

Recent Examples on the Web The Federal Aviation Agency study notes that kids, especially those under the age of 4, have more flexible skeletons, more relaxed muscle tonus, and a higher proportion of subcutaneous fat, which helps protect internal organs. Dan Koeppel, Popular Mechanics, 14 Feb. 2021

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'tonus.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


New Latin, from Latin, tension, tone

First Known Use

1876, in the meaning defined above

Time Traveler
The first known use of tonus was in 1876

Dictionary Entries Near tonus

Cite this Entry

“Tonus.” Dictionary, Merriam-Webster, Accessed 21 Sep. 2023.

Medical Definition


to·​nus ˈtō-nəs How to pronounce tonus (audio)
: a state of partial contraction that is characteristic of normal muscle, is maintained at least in part by a continuous bombardment of motor impulses originating reflexly, and serves to maintain body posture

called also muscle tone

compare clonus
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