WHAT has compiling a dictionary got in common with compiling a crossword puzzle? The two might seem very different activities - one heavy and serious, the other light and fun - but in fact they have much in common. Both deal exclusively in words, one leading to another. The difference is that one is serious business and the other is a game. One takes you to words in as quick, simple and direct a way as possible, while the other deliberately hides words behind more words. Jonathan Crowther knows all about the difficulties and joys of both tasks. He is editor of the latest edition of the Oxford Advanced Learner's Dictionary, and he has compiled the Observer Magazine's weekly crossword for over 20 years. 'English crosswords can be quite cryptic,' Mr Crowther says. 'The clues are quite complicated. They're like little word puzzles in which you try to set yourself a sort of challenge. And you can make it as difficult or easy as you choose, depending on what people want. 'In my case, I make them quite difficult because my puzzle is for those who look for a real challenge. So I have to do some wrap-up work, to confuse people a bit, and then they have to untangle the clues.' Dictionary-making, however, is quite the opposite. 'You're trying to make things as clear as possible, and using language to do it. But I find the two activities complement each other quite nicely. One is a useful escape from the other.' As editor of the dictionary, Mr Crowther said his main task was to overlook the project and to ensure a smoothness and consistency of style in the entire work. Fifteen freelance writers and special advisers worked on the dictionary as a team. 'Usually the freelance writers do the first draft of entries, and when their work is done, you don't need them any more. 'Then the work comes more into the publishing house, and we have a smaller team of editors working full-time on the project. 'The difficult part is putting together the work of the freelancers and making sure the overall style is consistent. If you don't, the dictionary would end up looking like the work of 10 or 12 people.' Special advisers on subjects like phonetics, American English and grammar were also involved. The dictionary took four years to produce - 'from concepts to finishing'. The initial stage, when the team worked out the editorial plan, took six months. The actual writing phase took another two-and-a-half years, while the editing stage took a year during which the team polished the entries and put all the parts together. 'Not everybody, I think, would find dictionary-making a pleasant way of spending their time,' Mr Crowther said. 'It is very slow, and you have to be meticulous.' Mr Crowther has also compiled four graded crossword books for learners in English, all published by the Oxford University Press.