"(as|) bald as an eagle" の定義と意味

What is the origin of the idiom "bald as an eagle" and when to use it?

The idiom "bald as an eagle" draws a comparison between someone who is completely bald and the baldness of an eagle. Eagles are known for their distinctive bald heads, where their feathers do not grow. This comparison emphasizes the complete lack of hair on the person's head. It is used to describe someone who has little to no hair on their head, typically due to natural hair loss or shaving. This idiom is often used in a descriptive or observational manner and can be used both affectionately and humorously.