1
: of, relating to, or being muscular contraction in the absence of significant resistance, with marked shortening of muscle fibers, and without great increase in muscle tone compare isometric
2
: isosmotic
—used of solutions

Examples of isotonic in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Sets were littered with ice coolers and sachets of isotonic powder. — Charlie Campbell, TIME, 24 Jan. 2025 Cleansing with paint thinner and isotonic saline solution was necessary. — Discover Magazine, 19 Nov. 2019

Word History

Etymology

International Scientific Vocabulary

First Known Use

1891, in the meaning defined at sense 1

Time Traveler
The first known use of isotonic was in 1891

Browse Nearby Words

Cite this Entry

“Isotonic.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/isotonic. Accessed 4 Oct. 2026.

Medical Definition

isotonic

adjective
1
: of, relating to, or exhibiting equal osmotic pressure
isotonic solutions
compare hypertonic sense 2, hypotonic sense 2
2
: of, relating to, or being muscular contraction in the absence of significant resistance, with marked shortening of muscle fibers, and without great increase in muscle tone compare isometric sense 2
isotonicity noun
plural isotonicities
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!