To beware is to be cautious and on your guard. The riskier the situation, the more you need to beware. A "Beware of the dog" sign means there's a dog in the house who doesn't care for visitors or new people. When you beware, you become very cautious. You look both ways and use extreme caution. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.