pernix

Etymology
Connected with, though the expected form would be.

Adjective

 * 1) nimble, agile
 * 2) swift

Usage notes
According to Döderlein, and  mean "swift, fast, quick"  in terms of quick motion (in general) with  as their antonym. More specifically, citus refers to a lively motion, whereas celer refers to an eager or impetuous motion.

On the other hand, pernīx and as "quick" denote a level of athletic nimbleness in terms of bodily activity, with  as their antonym. More specifically, pernīx involves a level of dexterity and quickness in an eclectic range of actions (such as climbing, hurdling, jumping, vaulting, etc.); whereas vēlōx is especially used for running, swimming and flying (moving in a direction)

Thirdly, and  as "quick" refer specifically to one's speed in terms of the shortest time to reach a destination, with  as their antonym. More specifically, festīnus intimates a certain level of impatience, whereas properus simply indicates a haste from energy simply.