I think that it would be a ballerina. Or a bumblebee.
I believe the best place to get a halloween costume is from Party City.
If you are looking information on what would be a good alien costume for Halloween, the best site is on costumezone.com/, they will give you the best costumes.
If you are looking for more information on where can you find a cheerleader costume for Halloween, the best place to look is on www.costumecraze.com/Traditional-Costumes-Cheerleader-Costume.
Part city
the headless horseman
Probably ghost costume. Or ghost detector
There are literally dozens of different halloween costumes available for your son. One of the best costumes is actually the costume of a cowboy.
moster high
As long as it is not past Halloween, it isn't too late to get a costume. Costume stores are open on Halloween and days before.
During the Halloween season, I find the best place to go for costumes with the biggest selection is Party City. They transform over half of their store into a Halloween costume showcase.
Umpire is a Halloween costume. It begins with the letter u.
Pirate, Vampire, Pumpkin, Zombie, Superheroes, Angel......