Obsessional (adjective)

Relating to or characterized by obsession; excessively preoccupied with a particular subject or idea.

Origin:

Derived from the word "obsession" meaning "an idea or thought that continually preoccupies or intrudes on a person"s mind", it was first recorded in the late 19th century.

Examples:

1. He had an obsessional interest in trains, and spent all his free time studying them.
2. Her obsessional behavior caused her to check and recheck the locks on her doors repeatedly.
3. His obsessional cleaning made it difficult for anyone to visit his home.
4. She had an obsessional fear of germs and would not touch anything without first cleaning it.
5. His obsessional need for order made it hard for him to function in a chaotic environment.