Definition of "landsman"

So, deprived of one leg, and the strange ship of course being altogether unsupplied with the kindly invention, Ahab now found himself abjectly reduced to a clumsy landsman again; hopelessly eyeing the uncertain changeful height he could hardly hope to attain.

1851 November 14, Herman Melville, “Leg and Arm. The Pequod, of Nantucket, Meets the Samuel Enderby, of London.”, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley, page 486

If the landsman should wish the gang-plank moved a foot farther forward, he would probably say: “James, or William, one of you push that plank forward, please”; but put the mate in his place, and he would roar out: “Here, now, start that gang-plank for'ard! Lively, now! What're you about!..."

1883, Mark Twain, Life on the Mississippi

When I returned again to life, the same uproar, the same confused and violent movements, shook and deafened me; and presently, to my other pains and distresses, there was added the sickness of an unused landsman on the sea.

1886 May 1 – July 31, Robert Louis Stevenson, Kidnapped, being Memoirs of the Adventures of David Balfour in the Year 1751: […], London, Paris: Cassell & Company, published 1886