1. Vigilant
   "on guard against con artists"
   - on one's guard, upon one's guard, on your guard

See also: wary

• antiviral agent
• antiviral drug
• antivirus
• antivivisectionist
• antler
• antler moth
• antler-like
• antlered
• Antlia
• antlion
• antlion fly
• Antofagasta
• Antoine Domino
• Antoine Henri Becquerel
• Antoine Laurent de Jussieu
• Antoine Laurent Lavoisier
• Antoine Lavoisier
• Anton Bruckner
• Anton Chekhov
• Anton Chekov
• Anton Gregor Rubinstein
• Anton Grigorevich Rubinstein
• Anton Pavlovich Chekhov
• Anton Pavlovich Chekov
• Anton Rubenstein