From Proto-Indo-European *h₂weh₁-lo- (“wind”), from *h₂weh₁- (“to blow”), named after the speed of wind.[1]
Older theories derive the word from Proto-Italic *weksloks, from Proto-Indo-European *weǵʰ- (“to bring, transport”) (whence vehō).
vēlōx (genitive vēlōcis, comparative vēlōcior, superlative vēlocissimus, adverb vēlōciter); third-declension one-termination adjective
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, vēlōx and pernīx 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.
| singular | plural | ||||
|---|---|---|---|---|---|
| masc./fem. | neuter | masc./fem. | neuter | ||
| nominative | vēlōx | vēlōcēs | vēlōcia | ||
| genitive | vēlōcis | vēlōcium | |||
| dative | vēlōcī | vēlōcibus | |||
| accusative | vēlōcem | vēlōx | vēlōcēs | vēlōcia | |
| ablative | vēlōcī | vēlōcibus | |||
| vocative | vēlōx | vēlōcēs | vēlōcia | ||