1. incentive stock option.
2. International Standardization Organization.
3. the numerical exposure index of a photographic film under the system adopted by the International Standardization Organization, used to indicate the light sensitivity of the film's emulsion.
a combining form meaning “equal,” used in the formation of compound words: isochromatic; in chemistry, used in the names of substances which are isomeric with the substance denoted by the base word: isocyanic acid. Also, esp. before a vowel,is-.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.