Definition of "fitfully"

The cabin lamp—taking long swings this way and that— was burning fitfully, and casting fitful shadows upon the old man’s bolted door […]

1851 November 14, Herman Melville, chapter 123, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley

The train for Marmion left Boston at four o'clock in the afternoon, and rambled fitfully toward the southern cape, while the shadows grew long in the stony pastures […]

1886, Henry James, chapter XXXV, in The Bostonians, London, New York, N.Y.: Macmillan and Co.

We shivered miserably throughout the night. Now and again fitfully slept, but the pain of the cold always aroused me.

1904, Jack London, chapter 36, in The Sea-Wolf (Macmillan’s Standard Library), New York, N.Y.: Grosset & Dunlap