Meaning
To “turn a blind eye” to something means to pretend not to have noticed it.
Example
“She took one of the cookies, but I turned a blind eye.”
Origins
Interestingly, this expression is said to have arisen as a result of the famous English naval hero Admiral Horatio Nelson, who, during the Battle of Copenhagen in 1801, is alleged to have deliberately raised his telescope to his blind eye, thus ensuring that he would not see any signal from his superior giving him discretion to withdraw from the battle.
