(1) Having a greater degree of tone, tension or tonicity
(2) Having a greater osmotic pressure in a fluid compared to another fluid
Hypertonic is a descriptive word relating to hypertonicity. In cellular level, hypertonicity may pertain to a property of a solution with a comparatively greater solute concentration than that in another solution. A solution is also described as hypertonic when the other solution being compared with has greater osmotic pressure in a fluid than the other fluid. Hypertonic may also pertain to a condition or property of a solution that has greater degree of tonicity than the other solution. Solutions that have different tonicities will result in a net flow of water across the cell membrane. For example, blood serum that is hypertonic to a physiologic salt solution would result in the net movement of water molecules towards the area with less water concentration (or higher solute concentration) (i.e. towards the blood serum).
In the tissue level, a hypertonic muscle is characterized by having a greater degree of tone or tension while its length changes. This is in contrast to a hypotonic muscle that has a lesser degree of tone or tension. A muscle whose tension remains relatively constant indicates isotonicity.
Word origin: hyper– (“over”) + Greek tonos (“tension”) + –ic