According to our lexicographer Ian Brookes (former editor-in-chief of The Chambers Dictionary), a large, one volume English dictionary can contain upwards of 230,000 words. But the English language creates many words by adding various endings to a core word. For example, if we know what 'snow' means, we can work out 'snowy', 'snowing', and 'snowstorm'. If we whittle the dictionary down then to their core words, a large dictionary will have about 42,000 core words. Of those core words, 32,000 are technical words, regional words and obscure words that many of us don't use, unless we are scientists, academics, crossword enthusiasts, or Scrabble players. That leaves us with about 10,000 of the core words that form part of the general vocabulary of English.
These 10,000 words provide a basis to excel in reading, writing and speaking. It won't just help in English and literacy, but in other academic subjects as well.