Which clue?

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Across
  1. 1. a colored usually liquid material for writing and printing
  2. 2. to make a drawing, pattern or sketch of
  3. 6. capacity to endure pain or hardship
  4. 7. to pierce with or as if with a pointed instrument or object
  5. 10. one thickness, course or fold laid over or under another
  6. 11. designed to be used once or a limited number of times
  7. 13. to keep secret or shut off from view
  8. 14. lacking sharpness of edge or point
  9. 15. items needed for the performance of a task or activity
Down
  1. 1. to force fluid into
  2. 3. causing intense mental or physical distress
  3. 4. worked or done by hand
  4. 5. to free from all viable microorganisms
  5. 8. an extremely thin, solid instrument inserted through the skin
  6. 9. the getting rid of whatever is unwanted or useless
  7. 12. not easily removed, washed away or erased