mizzenmast

noun3

1. •
   The aftmost mast on a ship having three masts; the third-tallest mast on a full-rigged ship.
2. •
   The third-foremost mast on a ship having more than three masts.
3. •
   The second mast of a ship having two masts where the second one is shorter, such as a ketch or yawl.