noun

• (countable) A country's entire maritime military force, including ships and personnel.
  "The skipper Mr. Cooke had hired at Far Harbor was a God-fearing man with a luke warm interest in his new billet and employer, and had only been prevailed upon to take charge of the yacht after the offer of an emolument equal to half a year's sea pay of an ensign in the navy."
• (countable) A governmental department in charge of a country's maritime military force.
• (archaic, countable) Any fleet of maritime vessels, and especially the entire fleet of any particular nationality, including vessels that are commercial, military, or both.
• (countable and uncountable) A dark blue colour, usually called navy blue.

adj

• (military) Belonging to the navy; typical of the navy.
  "[…] there are chess ships and checker ships and those where acey-deucey is almost the only game, the sailors' own improved version of backgammon. Fliers from the seacoast of Iowa, anxious to be as navy as the rest, are usually the first to pick it up."