The Oxford Phrasal Academic Lexicon (OPAL) is a set of four word lists, which you can download as PDFs:

  1. Written single words (1200 words)
  2. Spoken single words (600 words)
  3. Written phrases (370 phrases)
  4. Spoken phrases (250 phrases)

According to Oxford, these are the most important words to know in academic English.

You can also view the words and phrases online and look up definitions, collocations, etc. The phrases can be filtered by functions, such as adding, comparing, defining, hedging and making contrasts.

An opal is “a white or almost clear semi-precious stone in which changes of colour are seen, used in jewellery”.