1. double helix a pair of parallel helices intertwined about a common axis
  2. double-glaze provide with two sheets of glass
  3. double obelisk a character used in printing to indicate a cross reference or footnote
  4. duplex a house with two units sharing a common wall
  5. double check something that checks the correctness of a previous check
  6. double-check check once more to be absolutely sure
  7. double talk deliberately unintelligible gibberish
  8. double digit a two-digit integer; from 10 to 99
  9. double chin a fold of fatty tissue under the chin
  10. double gold very tall branching herb with showy much-doubled yellow flower heads
  11. double-decker a vehicle carrying many passengers
  12. double cross an act of betrayal
  13. double take a delayed reaction indicating surprise
  14. double-dealing acting in bad faith
  15. double bass largest and lowest member of the violin family
  16. double-space type with a full space between lines
  17. double eagle a former gold coin in the United States worth 20 dollars
  18. double bogey to shoot two strokes over par
  19. double back retrace one's course
  20. double-quick (of a marching cadence) very quick