Descriptive of hair bristling or standing up as on one's arms typically caused by a sudden jolt or a surprise: When Rodney and Jeff were riding home on the bus after school, the driver had to make a sudden swerve to avoid hitting a car that made a sudden stop in front of it, which caused a horrent reaction among everyone on the bus.

Mrs. Smith, the manager, made a discovery that caused a horrent reaction on her arms when she saw that the office computer had been stolen during the night.