at the boundary
Antonyms
Examples
Extreme seductiveness is at the boundary of horror.
Enjoyment appears at the boundary between boredom and anxiety, when the challenges are just balanced with the person's capacity to act.
Rose pictured him standing at the boundary of the Ogletree house in that enormous fur cape, with a giant sword sticking over his shoulder, roaring at the top of his lungs and then being upset that nobody came out, and laughed.