This can mean:

• The African nation of Côte d'Ivoire
• cI, the repressor cI protein.
• The postnominal of a Companion of the Order of the Crown of India
• Abbreviation for Confidential Informant
• Christmas Island, territory of Australia
• Kiritimati, another island by the name of "Christmas Island", and a Pacific atoll
• Cocos (Keeling) Islands, territory of Australia
• Cocos Island, offshore island of the Republic of Costa Rica
• the IATA code for China Airlines
• Composite Leading Indicator

Ci is

1. the symbol for the Curie, a unit of radioactivity
2. a form of Chinese lyric poetry
3. abbreviation for the TV series Law_&_Order:_Criminal_Intent
4. Tongyong Pinyin for Qi
5. the symbol for the Cosine integral