surface tension

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane.
2. n. A measure of this property.

Century Dictionary and Cyclopedia

1. n. The tension of the surface-film of a liquid due to cohesion. This serves to explain many of the phenomena of capillarity.

Wiktionary

1. n. physics the effect on the surface of a liquid that makes it behave as a stretched elastic membrane; it is caused by unbalanced intermolecular forces
2. n. physics a measure of this effect

GNU Webster's 1913

1. (Physics) That property, due to molecular forces, which exists in the surface film of all liquids and tends to bring the contained volume into a form having the least superficial area. The thickness of this film, amounting to less than a thousandth of a millimeter, is considered to equal the radius of the sphere of molecular action, that is, the greatest distance at which there is cohesion between two particles. Particles lying below this film, being equally acted on from all sides, are in equilibrium as to forces of cohesion, but those in the film are on the whole attracted inward, and tension results.

WordNet 3.0

1. n. a phenomenon at the surface of a liquid caused by intermolecular forces