C9, C09 or C-9 may refer to:

Biology, medicine, and chemistry

* C9 (

Complement component 9 Complement component 9 (C9) is a MACPF protein involved in the complement system, which is part of the innate immune system. Once activated, about 12-18 molecules of C9 polymerize to form pores in target cell membranes, causing lysis and cell dea ...

), a protein * ATC code C09, a subgroup of the Anatomical Therapeutic Chemical Classification System * C09, ICD-10 code for malignant neoplasm of tonsil * Carbon-9 (C-9 or ⁹C), an isotope of carbon

Military and weapons

* Hi-Point Models C9 and C9 Comp handguns *

C9 LMG The FN Minimi (short for french: Mini Mitrailleuse; "mini machine gun") is a Belgian 5.56mm light machine gun/squad automatic weapon developed by Ernest Vervier for FN Herstal. First introduced in the late 1970s, it is now in service in more tha ...

, Canadian light machine gun * C9, an ID for the German ''Nachtjagdgeschwader'' 5 air squadron in World War II

Music

* C9, a note five octaves above Middle C * C9, a C

ninth chord In music theory, a ninth chord is a chord that encompasses the interval of a ninth when arranged in close position with the root in the bass. Heinrich Schenker and also Nikolai Rimsky-Korsakov allowed the substitution of the dominant seve ...

Organizations

Cloud9 Cloud9 Esports, Inc., or simply Cloud9 (C9), is an American professional esports company based in Santa Monica, California. The company was originally founded as a professional ''League of Legends'' team by Jack and Paullie Etienne in May 2013 ...

, an American esports organization * C9 League, an association of Chinese universities * The

Council of Cardinal Advisers The Council of Cardinals (called C9 due to the fact it contained 9 cardinal members for some time), also known as the Council of Cardinal Advisers, is a group of cardinals of the Catholic Church appointed by Pope Francis to serve as his adviser ...

, an advisory body to the pope, originally comprising nine members *

C9 Entertainment C9 Entertainment () is a South Korean entertainment agency founded in 2012 by Kim Dae-soon. The company operates as a record label, talent agency, music production company and event management. The company was a subsidiary of Claire's Korea, par ...

, a South Korean entertainment company and record label

Transportation

Cierva C.9 __NOTOC__ The Cierva C.9 was an experimental autogyro built by Cierva in England in 1927, in association with Avro AVRO, short for Algemene Vereniging Radio Omroep ("General Association of Radio Broadcasting"), was a Dutch public broadcas ...

, a 1927 British experimental autogyro * HMS ''C9'', a British submarine * Ford C-9, a US military designation for the Ford Trimotor aircraft *

McDonnell Douglas C-9 The McDonnell Douglas C-9 was a military version of the McDonnell Douglas DC-9 airliner. It was produced as the C-9A Nightingale for the United States Air Force, and the C-9B Skytrain II for the United States Navy, U.S. Navy and United States Ma ...

, a US Air Force transport aircraft based on the civilian DC-9 * USS ''Montgomery'' (C-9), a US Navy cruiser * C9, the IATA code for

Cirrus Airlines Cirrus Airlines Luftfahrtgesellschaft mbH was a German regional airline with its head office in Hallbergmoos and its maintenance facilities at Saarbrücken Airport. It operated both charter and scheduled flights, the latter on behalf of Lufthan ...

Sauber C9 The Sauber C9 (later named the Sauber Mercedes C9 or Mercedes-Benz C9) is a Group C prototype race car introduced in 1987 as a continuation of the partnership between Sauber as a constructor and Mercedes-Benz as an engine builder for the World Sp ...

, a Le Mans racing car * C9 engine, by

Caterpillar Inc. Caterpillar Inc. (stock symbol CAT) is an American ''Fortune'' 500 corporation and the world's largest construction-equipment manufacturer. In 2018, Caterpillar was ranked number 65 on the ''Fortune'' 500 list and number 238 on the Global ''Fo ...

* C-9 (Cercanías Madrid), a commuter rail line in

Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a metropolitan area population of approximately 6.7 million. It is the second-largest city in the European Union (EU), and ...

Other uses

* C9, an

ISO 216 ISO 216 is an international standard for paper sizes, used around the world except in North America and parts of Latin America. The standard defines the "A", "B" and "C" series of paper sizes, including A4, the most commonly available paper size ...

standard paper size * C9, a holiday light bulb size * C9, a sportswear line by