Great idea, Alexandra

I will start off with a few that I think are relatively important ;):
Barre - pronounced bar ( I put this in because a LOT of people misspell this word)
Plié - plee AY; bending movement, as in demi plié and grande plié
Tendu - tahn dew; from etendre, to stretch. It is a stretch of the foot to a pointed position in front, side or back.
Dégagé - day gah ZHAY; also known as glissé or battement jeté. An elongated tendu, one which disengages from the floor.
Rond de jambe - rond duh zhamb; round of the leg. The working leg moves in a circular motion, either front to back (en dehors) or back to front (en dedans).
En dehors - on duh OR; outward, moving away from center, or front to back
En dedans - on duh DAHN; inward, moving towards the center, or back to front
Port de bras - por duh bra; carriage of the arms
Fondu - just as it looks, fondu; melting acting, as in bending on one leg into a demi plié
Frappé - frap AY; to strike. An exercise at the barre for quick ankle and knee motion. Can be done with an actual strike on the floor with the ball of the foot, or with a pointed foot. Different methods do this exercise rather differently.
Retiré- ruh tee RAY; withdraw. A position of the working leg with the toe on the knee of the supporting leg, used for pirouettes and pointe work and on the way to a developpé.
Developpé - dev low PAY; to unfold or develop. Leg moves from 5th with toe sliding up the leg to the knee and then unfolding outward to the front, the side, or the back.
Petit Battement - puh tee bat mahn; small beats. Working foot moves very quickly back and front around the ankle in a sur le cou de pied position.
Grand Battement - grand bat mahn; big beats

An overgrown dégagé! Working leg goes through tendu and dégagé and is "thrown", or lifted, to a position as high as possible (within reason of course ;)), and comes down through the tendu and into the 5th position.