The Highest Mast on a Ship
Puzzle 9 of Endangered Species Pack
Question is: The Highest Mast on a Ship
and the answer is: TOPSAIL
Word Meaning:
TOPSAIL — (nautical) A sail or either of the two sails rigged just above the course sail and supported by the topmast on a square-rigged sailing ship.
Definitions from Wiktionary.