"place where an army lodges temporarily," 1520s, from French camp, from Italian campo, from Latin campus "open field, level space" (also source of French champ; see campus), especially "open space for military exercise."
A later reborrowing of the Latin word, which had been taken up in early West Germanic as *kampo-z and appeared originally in Old English as camp "contest, battle, fight, war." This was obsolete by mid-15c. Transferred to non-military senses 1550s. Meaning "body of adherents of a doctrine or cause" is 1871. Camp-follower first attested 1810. Camp-meeting is from 1809, originally usually in reference to Methodists.