Time: 5 to 10 minutes.
This is one of my favorite TEFL games for practicing defining relative clauses. Write a list of definitions for four or five nouns. Choose nouns with the same first letter. Give the students the clues, and they must decide - in pairs, groups, or as a whole class - what the original nouns were, and the shared initial letter.
An example for an advanced ESL lesson might be: "A novel which tells the story of a zombie private eye," "The god of the sea who gave his name to a large planet," "The country where hobbits have been seen."
The answers, of course, being 'N.' Necropolis (written by Tim Waggoner), Neptune and New Zealand. Much easier examples should be given when teaching English to kids. "An animal that gives us milk," "A bird we eat that cannot fly," for example [cow & chicken].
After you have demonstrated the activity, the students can write their own examples in pairs. With lower level classes, you can give a list of nouns for them to define. This also makes a good homework activity which can then be read out for guessing, as a warmer in the following class.