The Probert Encyclopaedia of Music

ANTHEM

An anthem was originally a hymn sung in alternate parts. In later usage the term applied to a sacred tune or piece of music set to words taken from the Psalms or other parts of the Scriptures, in modern times the term generally applies to a national song. Anthems were first introduced into church service in Elizabeth I's reign as a developed motet. The original anthems could be for one, two, or any number of voices, but seldom exceeded five parts, and may or may not have had an organ accompaniment written for them.
Research Anthem