Of or pertaining to a solution (e.g. extracelllular fluid) with higher solute concentration compared with another. (see: hypotonic, isotonic). For example, if the extracellular fluid has greater amounts of solutes than the cytoplasm, the extracellular fluid is said to be hypertonic.
A cell placed in a highly concentrated solution will result in the water molecules diffusing out of the cell. Eventually, the cell will shrink. It should be noted, however, that not all cells in a hypertonic solution will shrink. The cells have ways to circumvent hypertonicity (see osmoregulation).