pernix

Connected with perna (“ham, haunch”), though the expected form would be *pernāx.[1][2]

• (Classical) IPA^(key): /ˈper.niːks/, [ˈpɛrniːks̠]
• (modern Italianate Ecclesiastical) IPA^(key): /ˈper.niks/, [ˈpɛrniks]

pernīx (genitive pernīcis, comparative pernīcior, superlative pernīcissimus, adverb pernīciter); third-declension one-termination adjective

1. nimble, agile
2. swift
   • 29 BCE – 19 BCE, Virgil, Aeneid 4.180:

     pernīcibus ālīs

     with swift wings

According to Döderlein, celer and citus mean "swift, fast, quick" in terms of quick motion (in general) with tardus 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 vēlōx as "quick" denote a level of athletic nimbleness in terms of bodily activity, with lentus 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, properus and festīnus as "quick" refer specifically to one's speed in terms of the shortest time to reach a destination, with sēgnis as their antonym. More specifically, festīnus intimates a certain level of impatience, whereas properus simply indicates a haste from energy simply.

Third-declension one-termination adjective.

• pernīcitās
• pernīciter

• “pernix”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• “pernix”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
• pernix in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.