Before starting, it is a good idea to revise ways of giving definitions for words. Write some useful phrases on the board. What phrases you use will depend upon the type of words are in your crossword. Here are some ideas:
Demonstrate the activity by asking students to guess what word you are describing using the useful phrases, e.g.
Ask students to give definitions for one or two other common words to practise using the phrases. Divide the class into two groups, As and Bs. Hand out worksheets A and B to the appropiate students. Give students time to look at the words they are going to have to describe. If necessary, give individual help at this stage. Reorganise the classroom so that Student As and Bs are facing each other working in pairs. Make it clear that their worksheet is a secret from their partner. Explain that they have to take turns to ask for a word that is missing from their crossword. They simply ask:
Their partner must try and explain the word to them.
Set a definite time limit (e.g. 25 mins) and stop the students at the end of it, whether they have finished or not. Finish the activity by showing the students the answers on the board or by giving them the answers on a piece of paper. You can also clarify the meaning / pronunciation of any words that students had problems with.