"Words, words, words" says Hamlet. You can't really do language without them, and a tool of a competent writer is knowing a) what a word means and b) how to combine it with other words.
Key stage 3 pupils are confronted with dozens of new words each day, all demanding to be stored away in memory together with their meanings. If they don't already know the meaning, they have to discover it. So they either guess, or look it up in a dictionary.
Dictionaries are pretty daunting for KS3 pupils, and not least in the definitions themselves. The trouble is that, however accessible they try to be, dictionary definitions are written in a special kind of English, and, like any other genre, this kind of English can be confusing to the novice.
If you know how to read a definition, then you know not to take the wording too seriously. For example, take the word "ally". Several reputable dictionaries say that an ally "helps and supports" another person or country. But how is helping and supporting different from just helping? Or again, for "anomaly" we find it's different from what is "normal or usual"; but "normal" and "usual" mean the same. Worse still, the same dictionary contrasts the "anomalous" with what is merely "normal" (and not "usual").
Pity the poor students who are picking their way through these definitions.
Why not simply define "anomalous" as a formal synonym of "unusual", thereby giving them a sense of how word choice varies by context? This definition is likely to be a great deal more helpful for anyone who already knows the word "unusual".
For so many pupils, using dictionaries can be a daunting and alienating task, something which ends up undermining their self-confidence. A really helpful activity for a KS3 class is to look in detail at a few definitions in some available dictionary. If you can provide a copy for each pair of pupils, so much the better. Let them choose a page, then let them look for definitions where words are redundant (like our "helps and supports") or where closely related words are given unrelated definitions (like the case of "anomalous" and "anomaly"). Invite them to imagine how these flaws crept into the dictionary, and let them see the lexicographer - Dr Johnson's "harmless drudge" - behind the definitions. How different from the common view of "the dictionary" as the ultimate truth on words. All this leads up to the fun part where they write their own definitions of words in areas where they themselves are "experts" - everyday words such as "walk" or "read". All being well, they'll then read other people's definitions with more understanding and sympathy and less awe.