Err/er/ Definition 1 of 2Pro Tip 1/3Common Phrases Learn common expressions with 'err' to sound natural in conversation. To err is human; to forgive, divine. Pro Tip 2/3Caution Context 'Err on the side of caution' means to be especially careful rather than taking a risk. I'll err on the side of caution and bring an umbrella. Pro Tip 3/3Judgment Errors Using 'err' can imply a poor decision or error in judgment. He erred in trusting the unreliable data.