1. Vigilant
   - on guard, on one's guard, on your guard

See also: wary

• basic
• basic assumption
• basic cognitive process
• basic color
• coaling station
• coalition
• coalitionist
• coalman
• coalpit
• coaming
• coapt
• coaptation
• coarctate
• coarctation
• coarse
• coarse-furred
• coarse-grained
• coarse-haired
• coarse-textured
• coarsely
• coarsen
• coarsened
• coarseness
• coast
• coast banksia