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 The Hi-Point Model C-9 is a polymer-framed, semi-automatic, blowback-operated pistol manufactured by Hi-Point Firearms. It is chambered in 9×19mm Parabellum and is rated to accept +P ammunition. It became well known for its low retail price of ...

handguns *

C9 LMG The FN Minimi (short for ; "mini machine gun") is a Belgian 5.56×45mm NATO, 5.56mm or 7.62×51mm NATO, 7.62mm light machine gun, also classified as a squad automatic weapon developed by Ernest Vervier for FN Herstal. Introduced in the late 1970s ...

, 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 C or Do is the first note of the C major scale, the third note of the A minor scale (the relative minor of C major), and the fourth note (G, A, B, C) of the Guidonian hand, commonly pitched around 261.63 Hz. The actual frequency has d ...

* C9, a C

ninth chord In music theory, a ninth chord is a chord (music), chord that encompasses the interval (music), interval of a ninth when arranged in close and open harmony, close position with the root (chord), root in the bass (sound), bass. Heinrich Schenker ...

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 The C9 League is an inter-university seminar composed of nine public universities in China. It was established on May 4, 1998, at the 100th anniversary of Peking University. These elite universities are associated with academic excellence and ...

, an association of Chinese universities * The

Council of Cardinal Advisers The Council of Cardinals (, , ; also called C9 because it contained nine cardinal members for a time) or Council of Cardinal Advisers is a group of cardinals of the Catholic Church appointed by Pope Francis to serve as his advisers. The counci ...

, 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 is home to artists including Younha, Le ...

, 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 (an initialism of the founder's name) was a British aircraft manufacturer. Its designs include the Avro 504, used as ...

, a 1927 British experimental autogyro * HMS ''C9'', a British submarine *

Ford C-9 The Ford Trimotor (also called the "Tri-Motor", and nicknamed the "Tin Goose") is an American three-engined transport aircraft. Production started in 1925 by the companies of Henry Ford and ended on June 7, 1933, after 199 had been made. It wa ...

, a US military designation for the Ford Trimotor aircraft *

McDonnell Douglas C-9 The McDonnell Douglas C-9 is a retired 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 U.S. Navy and Marine Corps. The final flig ...

, 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 Lufthans ...

Sauber C9 The Sauber C9 (later named the Sauber Mercedes C9 or Mercedes-Benz C9) is a Group C prototype racing 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 ...

, a Le Mans racing car * C9 engine, by

Caterpillar Inc. Caterpillar Inc., also known as Cat, is an American construction, mining and other engineering equipment manufacturer. The company is the world's largest manufacturer of construction equipment. In 2018, Caterpillar was ranked number 73 on the ' ...

C-9 (Cercanías Madrid) Line C-9, formerly known as the Guadarrama Electric Railway (), is a narrow-gauge mountain railway incorporated into Madrid's Cercanías Madrid, Cercanías commuter rail network. The line is operated by Renfe Operadora and runs through the Guadar ...

, a commuter rail line in

Madrid Madrid ( ; ) is the capital and List of largest cities in Spain, most populous municipality of Spain. It has almost 3.5 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 7 million. It i ...

LNER Class C9 The NER Class Z (LNER Class C7) was an "Atlantic" class of locomotives designed by Vincent Raven. It was introduced in 1911. Construction and early life Vincent Raven had been appointed Chief Mechanical Engineer of the North Eastern Railway (N ...

, a class of 2 British steam locomotives rebuilt from C7s in 1931 *

SL C9 The SL Cx series is the collective designation for the C1–C15 types of metro trains used on the Stockholm Metro from 1950 until 2024. Over 800 Cx cars were built in total. They were manufactured by ASEA, Hägglund & Söner, and Svenska Järnv ...

, a type of rolling stock used in the Stockholm metro

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, which includes the A4, the most commonly availabl ...

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