An adder in your dream can represent something in your life that you perceive as evil.
This can be a person or an idea that you believe is threatening.
Pay attention to the way the adder is behaving in your dream. If it is behaving calmly, in a non-threatening way, your dream could be telling you that you are being paranoid, seeing threats where none exist or over exaggerating the severity of minor threats.
On the other hand, if the adder seems to appear suddenly, out of nowhere, your dream can be telling you that you need to be more alert to possible dangers.
Dreaming of an adder can mean that you are worried that your partner is or will be unfaithful.