1. Vigilant
   "must remain on your guard in such a situation"
   - on guard, on one's guard, upon one's guard

See also: wary

• expensively
• expensiveness
• experience
• experienced
• experient
• experiential
• experiment
• experimental
• experimental condition
• experimental extinction
• experimental method
• experimental procedure
• experimental psychology
• experimental variable
• experimentalism
• experimentally
• experimentation
• experimenter
• experimenter bias
• expert
• expert witness
• expertise
• expertly
• expertness
• expiable