Endless Alphabet is an iPad app ($5.99 as of December 2013) designed to help children learn to spell and learn the definitions of new words. The app features a different word for each letter of the alphabet. Each word is read to the child and then the child tries to spell each word by dragging and dropping the letters into place. When a word is spelled correctly an animation is played and the app’s narrator reads the definition of the word.
The name of the app is Endless Alphabet because it is supposed to be regularly updated with new words. In a 1:1 iPad environment, Endless Alphabet could be a good resource for generating new vocabulary lists for your students to learn.