Med. carcinoma in situ
• (or c.i.s.) cataloguing in source
• (USA ) Catholic Information Society
• (USA ) Center for International Studies
• Central Information Service on Occupational Health and Safety (of ROSPA)
• Chartered Institute of Secretaries (now Institute of Chartered Secretaries and Administrators)
• Coal Industry Society
• Med. combined-injury syndrome
• Commonwealth of Independent States (the former Soviet republics)
• CompuServe Information Service
• Cooperative Insurance Society