Macmillan distinguishes between these "red" words (which you should be able to use ) and "black" words (which you only need to recognize for reading).
While the full list is integrated into the printed and online dictionary, specific PDF summaries and pedagogical guides are often available: Usage Guides : Resources like the Macmillan Dictionary Red Words & Stars Pack provide practical activities for classroom use. Sample Lists : General overview PDFs and Scribd documents macmillan 7500 words list pdf
Linguists at Macmillan analyzed everything from newspapers and novels to conversations and lectures. They ranked every word based on (how often it appears) and range (how many different contexts it appears in). The top 7,500 words represent the vocabulary you need to understand 90% to 95% of general English texts. Macmillan distinguishes between these "red" words (which you