Here is a pfd file that contains 60 different "Word of the Week" words. These words are great to use for classroom transitions. You can also use this as a center, to have students research, define, and write a sentence about the word for the week. These words were chosen from Flocabulary.com.
4.L.4-Determine or clarify the meaning of unknown and multiple-meaning word and phrases based on grade 4 reading and content, choosing flexibility from a range of strategies.