Other forms: documentaries
A documentary is a film about something real — no actors, no lines written for the people in it. A camera following a fishing crew for a season, an hour on a murder case built from old news footage and interviews, a naturalist's voice over pictures of ants.
The word is a noun and an adjective at once: a documentary about the war, a documentary series, documentary footage. There is a second, drier use in law and history, where documentary evidence means evidence in the form of documents — papers rather than witnesses. Feature-length documentaries play in cinemas; a docudrama restages events with actors, which a documentary does not. Documentaries argue a case as hard as any opinion column, so real footage does not mean neutral.
1noundocumentaryA film or programme about real people and events, made with real footage and interviews.
“The documentary follows three families over ten years.”
2adjectiveconsistingConsisting of documents, or based on them.
“There is documentary evidence that the payment was made.”
documentary is a kind of film.
Documentary came from French documentaire, an adjective built on document, which goes back to Latin documentum. English has the same pieces to hand: document plus the ending -ary, as in ordinary and honorary. The film sense is the young one — the word described papers long before it described a camera.
Latin
documentum
French
documentaire
English, today
documentary
Borrowed from French documentaire. From French - adjective and (hence) noun documentaire, from document, from Latin documentum. Equivalent to document + -ary.
Etymology from Wiktionary, CC BY-SA