the act of replacing.

a person or thing that replaces another

summer replacements for vacationing staff; a replacement for a broken dish.

Military . a sailor, soldier, or airman assigned to fill a vacancy in a military unit.

Also called metasomatism. Geology . the process of practically simultaneous removal and deposition by which a new mineral grows in the body of an old one.

noun

alternate , stand-in , surrogate , reinstatement , restoration , substitute