- C1 stands for Methane
- C1 stands for Atlas (first cervical vertebra; common name)
- C1 stands for Canoe (one person)
- C1 stands for Capital One
- C1 stands for Composition 1 (plastic explosive)
- C1 stands for Capability 1
- C1 stands for Schedule I Controlled Substance (USA)
- C1 stands for Cyclopentolate 1% Eyedrops
- C1 stands for CPU State 1 (non-executing computing mode)
C1