A boundary or accepted division; a border.

“She lives on the borderline between reality and madness.”

An individual who has borderline personality disorder.

To border, or border on; to be physically close or conceptually akin to.

Nearly; not clearly on one side or the other of a border or boundary, ambiguous.

“I would rather hire a talented layman than a university graduate with borderline qualifications.”

Showing bad taste.

“Your borderline remarks about my aunt's dress destroyed my evening.”

Exhibiting borderline personality disorder.

Nearly; not entirely but nevertheless to a great extent

“He is borderline hypoglycemic and needs to monitor his sugar intake.”