Definition of "slily"

VVhen ſhe vvas dreſt, therefore, dovvn ſhe vvent, reſolved to encounter all the Horrours of the Day, and a moſt diſagreeable one it proved; for Lady Bellaſton took every opportunity very civilly and ſlily to inſult her; […]

1749, Henry Fielding, “In which Mrs. Miller Pays a Visit to Sophia”, in The History of Tom Jones, a Foundling, volume VI, London: A[ndrew] Millar, […], book XVII, page 134

So when they were working that evening at the pumps, there was on this head no small gamesomeness slily going on among them, as they stood with their feet continually overflowed by the rippling clear water; […]

1851 November 14, Herman Melville, “The Town-Ho’s Story (As Told at the Golden Inn.)”, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley, page 274

I lie there on the stretcher-bed and laugh slily, but say nothing; give vent to no opinion one way or the other.

1899, Knut Hamsun, “Part II”, in George Egerton [pseudonym; Mary Chavelita Dunne Bright], transl., Hunger […], London: Leonard Smithers and Co […], page 103