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The Collaborative International Dictionary
hypertonic

hypertonic \hy`per*ton"ic\, n. [Pref. hyper- + tonic.] (Physiology, Biochemistry) Having a higher osmotic pressure than a comparison solution; -- of an aqueous solution. Increasing the concentration of dissolved solids increases the osmotic pressure, and thus the tonicity of a solution. Opposite of hypotonic and contrasting with isotonic. [WordNet sense 1]

A knowledge of the colligative properties of solutions . . . is essential for one to understand fully the principles involved in rendering intravenous solutions isotonic with blood serum, or opthalmic solutions isotonic with lachrymal fluid. Solutions thus adjusted produce less shock and much less irritation than those which are hypotonic or hypertonic, and present-day practise recognizes the desirability of making the necessary adjustments whenever possible.
--Cook & Martin (Remington's Practice of Pharmacy, Tenth Ed.: Mack Publ., Easton Pa., 1951)

2. Specifically: Having an osmotic pressure greater than that of blood plasma, which is approximately that of a 0.2 normal solution of sodium chloride. Cells taken from a medium of normal physiological osmolality and placed in a hypertonic medium will shrink. [WordNet sense 1]

3. in a state of abnormally high tension; -- of muscle.

Syn: pumped-up.

Douglas Harper's Etymology Dictionary
hypertonic

1855, from hyper- + tonic. Related: Hypertonia; hypertonicity.

Wiktionary
hypertonic

a. 1 (context of a solution English) having a greater osmotic pressure than another 2 (context anatomy English) having a very high muscular tension; spastic

WordNet
hypertonic
  1. adj. (of living tissue) in a state of abnormally high tension; "hypertonic muscle tissue" [ant: hypotonic]

  2. (of a solution) having a higher osmotic pressure than a comparison solution [ant: hypotonic, isotonic]

Usage examples of "hypertonic".

He announced that he had taken great pains to avoid contamination: each meteorite he examined had been washed in twelve solutions, including peroxide, iodine, hypertonic saline and dilute acids.