Pas de cheval means the step of the horse. While a horse might seem an odd creature to emulate, they were an extremely important animal during the period that encompassed the formalization of ballet. Horses were transportation, status, work animals, and warriors. There were royal stables, and le Comte de Sissonne, for whom the step sissonne was named, began as a page of the royal stable (a great honor for him and his family). The rules of l’Équitation classique, classical rules of horse riding and training, were also formalized in the 17th century. In short, the horse and its movements were familiar to all, and the upper classes were trained in all of the arts: fencing, dance, music, oratory, horseback riding, and more.
Our modern translation of pas comes from the common usage. Un pas is a step of the foot or a figurative step. In ballet pas is slightly more complicated as it indicates the ensemble of small movements that make up a "step," as we now call it. In other words, pas de cheval is not a single movement but an ensemble of movements. Cheval means horse.
Pas de cheval is pronounced [pɑ də ʃ(ə)val]. Pas is pronounced like "pa" in the first syllable of the English papa. De is pronounced like you're practicing the sound a D makes in English. And cheval - sounds like "sh" + “vol” put together (“vol” as in the beginning of the word volleyball in English - our English vowels are a bit different but this is the closest equivalent).
Pas de cheval is a scooping movement often performed at the barre in conjunction with dégagé. The movement can begin in a crossed position (3rd or 5th) or from a battement that passes through a crossed position, the dancer’s working foot will slide further into a crossed position, with the ball of the working foot approaching the arch of the supporting foot as the heel of the lifted foot peels of the ground. The working foot moves through a cou-de-pied position (devant or derrière depending on the direction that the movement will travel and the pattern of the combination). Following this scoop to cou-de-pied, the working leg extends out from the cou-de-pied, touches the floor with a fully extended leg, and draws back into a crossed position (3rd or 5th) to close.
Even your youngest dancer can usually picture the way a horse paws at the ground, and this is excellent imagery for pas de cheval.
See the video below of a horse pawing at the ground.