I like dictionary.com, don't get me wrong...
but I much prefer ninja words.
Yes, you heard me, ninjawords.com
Here are screenshots as to why:
Try one: dictionary.com, "lightning" being the word of choice
Lots of junk, lots of ads...
Now, let's try the same word at ninjawords:
There's no junk for my students to get distracted by PLUS ninjawords is so much faster when loading. (As it should be, ninjas are mighty quick!) Additionally, you can review your past history which is helpful for students.
There's your tech tip of the week!