C9

C9, C09 or C-9 may refer to:

Biology, medicine, and chemistry

• C9 (Complement component 9), 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
• Coccinella novemnotata, the nine-spotted ladybug or C9, a species of lady beetle

Military and weapons

• Hi-Point Models C9 and C9 Comp handguns
• C9 LMG, 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

Organizations

• Cloud9, an American esports organization
• C9 League, an association of Chinese universities
• The Council of Cardinal Advisers, an advisory body to the pope, originally comprising nine members
• C9 Entertainment, a South Korean entertainment company and record label

Transportation

• Cierva C.9, 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, 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
• Sauber C9, a Le Mans racing car
• C9 engine, by Caterpillar Inc.
• C-9 (Cercanías Madrid), a commuter rail line in Madrid
• LNER Class C9, a class of 2 British steam locomotives rebuilt from C7s in 1931
• SL C9, a type of rolling stock used in the Stockholm metro
• Omoda C9, a Chinese mid-size crossover SUV

Other uses

• C9, an ISO 216 standard paper size
• C9, a holiday light bulb size
• C9, a sportswear line by Champion

See also

• 9C (disambiguation)