What is this?

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Across
  1. 1. the matter? What is wrong? / What is the problem?
  2. 6. car vehicle used by the police
  3. 9. a thing (not named or known)
  4. 12. back return to a place
  5. 13. a person (not named or known)
  6. 15. person who operates a vehicle
  7. 16. lost become unable to find the way
Down
  1. 2. once more; in addition
  2. 3. no longer have something; fail to keep
  3. 4. officer person who works for the police force
  4. 5. one more; a different one
  5. 7. not able to be found; gone
  6. 8. large truck used for carrying goods (British English)
  7. 10. list is identical in structure and style to the one previously provided and can be used directly for a crossword puzzle, vocabulary worksheet, or matching activity. If you would like any modifications—such as shorter definitions, American English equivalents (e.g., “truck” instead of “lorry”), or additional clues—please specify.
  8. 11. for try to find something or someone
  9. 14. have to; it is necessary