Denshi Jisho — Online Japanese dictionary

間違う まちがう to make a mistake; to be incorrect; to be mistaken
Common word, Godan verb with u ending 

You can also

Look up kanji details for 間違う.

Try a Yahoo Jisho search for 間違う .
Try a Goo Jisho search for 間違う .
Try a Google search for 間違う .