Turn a blind eye means to deliberately ignore something, especially when you know it is there. It does not refer to actual vision in normal use. Instead, it describes a choice not to notice or respond.
The expression is widely connected to Admiral Horatio Nelson. During the Battle of Copenhagen in 1801, Nelson was said to have put a telescope to his blind eye and claimed he could not see the signal ordering him to stop. He continued the attack. Whether every detail of the story is perfect or not, this is the famous explanation most people know.
Today, the phrase is used figuratively. For example, you might say, The manager turned a blind eye to repeated lateness. That means the manager knew about the problem but chose not to act.
- Literal meaning: about actual eyesight
- Idiomatic meaning: choosing to ignore something
- Example: They turned a blind eye to the damage
This makes the phrase useful when you want to describe intentional inaction, not simple failure to notice.