Dog-ear (verb)

1. To fold down the corner of a page of a book as a marker.
2. To damage the corner of a book.

Origin:

19th century: origin uncertain; perhaps from the practice of marking a page by folding the corner down, as a dog might do to a book.

Examples:

1. He dog-eared the page where he left off reading.
2. She dog-eared the pages of the recipe book for reference.
3. The book was dog-eared from constant use.
4. The pages were dog-eared from being carried around.
5. The book had been dog-eared so many times the corners were damaged.