C9

C9, C09 or C-9 may refer to:

• C9, written short handed as C9 because in Cantonese (the Chinese languages), C9 is pronounced as (C Nine) and it means housewife (師奶 in Chinese)
• C9, an international standard paper size (40×57 mm), defined in ISO 216
• C9 engine, by Caterpillar Inc.
• C9, a global group of nine leading economists based in Zürich, Switzerland
• C9 League, an association of nine top Chinese universities
• C9, an extremely high musical note five octaves above Middle C.
• C9, musical chord Ninth.
• Complement component 9, a protein involved in the complement system
• ATC code C09 Agents acting on the renin-angiotensin system, a subgroup of the Anatomical Therapeutic Chemical Classification System
• C09, Malignant neoplasm of tonsil ICD-10 code
• C9 Incandescent light bulb, used in Christmas lighting usually 3 inches Length, 1 1/8 inch Width, 7 watts

Transportation

• Cierva C.9, a 1927 British experimental autogyro
• HMS C9, a C-class submarine of the Royal Navy
• Ford C-9, U.S. military designation for a Ford Trimotor aircraft
• McDonnell Douglas C-9 (C-9A Nightingale/C-9B Skytrain II), a transport aircraft of the United States Air Force (Nightingale) or U.S. Naval Reserve and United States Marine Corps (Skytrain II). It is the military version of McDonnell Douglas DC-9
• USS Montgomery (C-9), a protected cruiser of the United States Navy
• C9, the IATA code for Cirrus Airlines

Weapons

• Hi-Point Models C9 and C9 Comp handguns
• C9 LMG, a Canadian variant of the FN MINIMI light machine gun