Etymology From Middle English slade (“low-lying ground, a valley; a flat grassy area, glade; hollows of clouds; a creek, stream; a channel”), from Old English slæd (“valley, glade”), from Proto-West Germanic *slad, from Proto-Germanic *sladą (“glen, valley”), of uncertain origin. Perhaps from Proto-Germanic *sladaną (“to glide, slip”) or Proto-Germanic *sladdaz (“to be slack, droop”). Compare Old Norse slóð (“track, trail”).
Yet he slow in the slade of men of armys mo than syxty with his hondys.1470–1485 (date produced), Thomas Malory, “(please specify the chapter)”, in [Le Morte Darthur], book V, [London: […] by William Caxton], published 31 July 1485, →OCLC; republished as H[einrich] Oskar Sommer, editor, Le Morte Darthur […], London: David Nutt, […], 1889, →OCLC:
The thick and well-growne fogge doth matt my smoother slades, And on the lower Leas, as on the higher Hades The daintie Clover growes (of grasse the onely silke) That makes each Udder strout abundantly with milke.1612, Michael Drayton, Poly-Olbion, song 13 p. 222:
The Bishop, wearing a gleaming cape of green and gold, raised his hand over the plough and the kneeling farmers: "God speed the plough: the beam and the mouldboard, the slade and the sidecap, the share and the coulters[…]in fair weather and foul, in success and disappointment, in rain and wind, or in frost and sunshine. God speed the plough."1945 January 29, “Pattern Prays”, in Time Magazine: