I've been practising how to define words in English. I've just realized that I always just help kids out with any word they might not know. However, this way is the easy way out. They won't always have me by their side. They need to be able to get around a word they can't think of in English. Instead of getting stuck and racking their brains in vain to recall the word, they had better explain what they mean, i.e. define the word.
This, I realize, is easier said than done. So I collected a bunch of weak attempts by my students to define some easy words. In this powerpoint I showed them how a bad definition could be ambiguous, and what they need to do to make them better. You can show the first few solutions, and when they get the hang of it, just let them improve the definitions by themselves.
Make them realize a definition is typically made up of
a category (with or without an adjective)
and the use of the object or more details about what makes it different from other things in that category