early 14c., "to value, assess;" late 14c. "to stretch out, lengthen," from Anglo-French estendre (late 13c.), Old French estendre "stretch out, extend, increase," from Latin extendere "stretch out," from ex- "out" (see ex-) + tendere "to stretch" (see tenet). Related: Extended; extending.
programming To add features to a program, especially through the use of hooks. "Extend" is very often used in the phrase "extend the functionality of a program." Plug-ins are one form of extension. (1997-06-21)