| City Year | City-building game | City-state |
| Ciutat de Palma | Civetone | CIVETS |
| Civettictis civetta | Civic intelligence | Civic political culture |
| Civics | Civil and political rights | Civil authority |
| Civil aviation | Civil Aviation Administration of China | Civil Aviation Affairs |
| Civil Aviation and Meteorological Authority of Yemen | Civil Aviation Authority (United Kingdom) | Civil code |
| Civil discourse | Civil disobedience | Civil engineering |
| Civil Guard (Spain) | Civil law (legal system) | Civil liberties |
| Civil registry | Civil rights referendum | Civil society |
| Civil uprising phase of the Syrian Civil War | Civil war in Afghanistan (1989-1992) | Civil war in Afghanistan (1989–92) |
| Civil war in Afghanistan (1992-1996) | Civil war in Afghanistan (1992–96) | Civil war in Afghanistan (1996-2001) |
| Civil war in Afghanistan (1996–2001) | Civil war in Tajikistan | Civil-military operations |
| Civilian | Civilian control of the military | Civilisées |
| Civilization | Civilization (series) | Civilization V |
| Civilization V: Brave New World | Civilized core | Civitas Popthensis |
| Cizre | CJ Parker (wrestler) | CJCUC |
| CKM matrix | Cl | Claddagh ring |
| Cladding (construction) | Cladistics | Cladium mariscus |
| Cladobranchia | Cladocera | Cladorhynchus |
| Cladorhynchus leucocephalus | Cladosporium | Cladrastis kentukea |
| Claflin, Kansas | Claiborne County, Tennessee | Claiborne Parish, Louisiana |
| Claim rights and liberty rights | Claimed moons of Earth | Clair Cameron Patterson |
| Claire City, South Dakota | Claire Danes | Claire Etcherelli |
| Claire Holt | Claire Lee Chennault | Claire Redfield |
| Clairmarais | Clairton, Pennsylvania | Clam AntiVirus |
| Clam Falls, Wisconsin | Clam Lake Township, Michigan | Clam Union Township, Michigan |
| Clamator | Clamator coromandus | Clamator glandarius |
| Clamator jacobinus | ClamAV | CLAMP |
| ClamWin | ClamWin Antivirus | Clancy Brown |
| Clandestine abuse | Clanga clanga | Clanga pomarina |
| Clangula hyemalis | Clans, Alpes-Maritimes | Clapper bridge |
| Clapperboard | Clara Barton | Clara Basiana |
| Clara Bow | Clara City, Minnesota | Clara Janés |
| Clara Khoury | Clara Zetkin | Clarabelle Cow |
| Clarín (Argentine newspaper) | Clare Boothe Luce | Clare County, Michigan |
| Clare, Iowa | Clare, Michigan | Clare, New York |
| Claremont, Illinois | Claremont, Minnesota | Claremont, New Hampshire |
| Claremont, North Carolina | Claremont, South Dakota | Claremont, Virginia |
| Claremore, Oklahoma | Clarence (2014 TV series) | Clarence Acuña |
| Clarence Day | Clarence Goodson | Clarence King |
| Clarence L. Johnson | Clarence Nash | Clarence Seedorf |
| Clarence Township, Michigan | Clarence Williams III | Clarence, Iowa |
| Clarence, New York | Clarendon Hills, Illinois | Clarendon Township, Michigan |
| Clarendon, Arkansas | Clarendon, New York | Clarendon, Quebec |
| Clarendon, Texas | Clarendon, Vermont | Clarias batrachus |
| Clariden | Clariidae | CLARINASE |
| Clarinda, Iowa | Clarinet | Clarington, Ohio |
| Clarion County, Pennsylvania | Clarion, Iowa | Clarissa, Minnesota |
| Clarithromycin | Clark County, Indiana | Clark County, Wisconsin |
| Clark Duke | Clark Gable | Clark International Airport |
| Clark Johnson | Clark L. Hull | Clark Township, Michigan |
| Clark, South Dakota | Clarkdale, Arizona | Clarke Carlisle |
| Clarke County, Alabama | Clarke's three laws | Clarkedale, Arkansas |
| Clarkesville, Georgia | Clarkfield, Minnesota | Clarkia amoena |
| Clarks Grove, Minnesota | Clarks Hill, Indiana | Clarks, Nebraska |
| Clarksburg, Massachusetts | Clarksburg, Ohio | Clarksburg, Tennessee |
| Clarksburg, West Virginia | Clarksdale, Mississippi | Clarkson, Kentucky |
| Clarkson, New York | Clarkston, Georgia | Clarkston, Michigan |
| Clarkston, Utah | Clarkston, Washington | Clarkstown, New York |
| Clarksville City, Texas | Clarksville, Allegany County, New York | Clarksville, Arkansas |
| Clarksville, Indiana | Clarksville, Iowa | Clarksville, Michigan |
| Clarksville, New Hampshire | Clarksville, Ohio | Clarksville, Tennessee |
| Clarksville, Texas | Clarksville, Virginia | Clarkton, North Carolina |
| Clarno, Wisconsin | Clarques | Clash of Civilizations |
| Clash of Clans | Clash of clans | Clash of Loyalties |
| Clash of the Titans (2010 film) | Clasper | Class (biology) |
| Class (computer programming) | Class conflict | Class consciousness |
| Class discrimination | Class in Marxist theory | Class struggle |
| Classes of computers | Classful network | Classic car |
| Classic metal | Classical antiquity | Classical architecture |
| Classical compound | Classical conditioning | Classical electromagnetism |
| Classical electron radius | Classical element | Classical liberalism |
| Classical limit | Classical mechanics | Classical order |
| Classical physics | Classical planet | Classicism |
| Classics | Classification of finite simple groups | Classification of mental disorders |
| Classification society | Classified advertising | Classless Inter-Domain Routing |
| Classroom | Classroom design | Clathrate hydrate |
| Clatonia, Nebraska | Clatskanie, Oregon | Claude Adrien Helvétius |
| Claude Étienne Savary | Claude Bernard | Claude Berri |
| Claude Cahen | Claude Chevalley | Claude Cohen-Tannoudji |
| Claude Dornier | Claude Etienne Savary | Claude Faraggi |
| Claude Frollo | Claude Gaspard Bachet de Méziriac | Claude Giroux |
| Claude Henri de Rouvroy, comte de Saint-Simon | Claude Joseph Rouget de Lisle | Claude Lévi-Strauss |
| Claude Le Roy | Claude Louis Berthollet | Claude Makélélé |
| Claude Nicolas Ledoux | Claude Puel | Claude Reignier Conder |
| Claude Rich | Claude Saumaise | Claude Shannon |
| Claude Simon | Claude, Texas | Claude-Arnaud Rivenet |
| Claude-Étienne Savary | Claude-Etienne Savary | Claude-Louis Navier |
| Claudette Colbert | Claudette Colvin | Claudia Cardinale |
| Claudia Ciesla | Claudia Pechstein | Claudia Schiffer |
| Claudio Bellucci | Claudio Biaggio | Claudio Bravo (footballer) |
| Claudio Caniggia | Claudio García | Claudio Gentile |
| Claudio Husaín | Claudio López (footballer) | Claudio Marchisio |
| Claudio Morel Rodríguez | Claudio Pizarro | Claudio Puglisi |
| Claudio Ranieri | Claudio Reyna | Claudio Sánchez-Albornoz |
| Claudio Sánchez-Albornoz y Menduiña | Claudio Suárez | Claudio Terzi |
| Claudiu Bleonț | Claudius | Claudius Bombarnac |
| Claudius Gothicus | Claudius James Rich | Claudius Salmasius |
| Claus Bo Larsen | Claus Jensen | Claus von Stauffenberg |
| Clauseneae | Clauseninae | Clausius–Clapeyron relation |
