Prefixes sub-, trans-, under-

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Across
  1. 4. an exchange or transfer of goods, services, or funds
  2. 7. acting or done in a secret or dishonest way
  3. 9. to place too low a value on
  4. 11. an underground railroad usually in a large city
  5. 12. having started and in progress
Down
  1. 1. the underside of a body or mass
  2. 2. to pay less than what is normal or required
  3. 3. to put or sink below the surface of water
  4. 5. to transfer from one place to another
  5. 6. a vessel that can be submerged and navigated under water
  6. 8. to change (something) completely
  7. 10. extending or going across a continent
  8. 12. weighing less than is usual or required