Definition of "plod"

The beast that bears me, tired with my woe,Plods dully on, to bear that weight in me,

1609, William Shakespeare, “Sonnet 50”, in Shake-speares Sonnets. […], London: By G[eorge] Eld for T[homas] T[horpe] and are to be sold by William Aspley

I remember him as if it were yesterday, as he came plodding to the inn door, his sea chest following behind him in a handbarrow;

1881–1882, Robert Louis Stevenson, chapter 1, in Treasure Island, London, Paris: Cassell & Company, published 14 November 1883, part I (The Old Buccaneer), page 1

Quest[ion]. Where was Ioseph?Answ[er]. It may be, he was playing the Carpenter abrode for all their three livings, but sure it is, he was not idlely plodding the streetes, much lesse tipling in the Taverne with our idle swingers.

1596, Henoch Clapham, A Briefe of the Bible‎, Edinburgh: Robert Walde-grave, page 127

[…] Speed thou to Lombard-street, / Or plod the gambling 'Change with busy feet, / 'Midst Bulls and Bears some false report to spread,

1799, Matthew Gregory Lewis, The Love of Gain, London: J. Bell, p. 50, lines 449-451

Break no rosemary, bright with rimeAnd sparkling to the cruel clime;Nor plod the winter land to lookFor willows in the icy brookTo cast them leafless round him […]

1896, A. E. Housman, A Shropshire Lad‎, London: The Richards Press, XLVI, pp. 69-70

Poore plodding schoolemen, they are farre too low, / which by probations, rules and axiom’s goe, / He must be still familiar with the skyes, / which notes the reuolutions of thine eyes;

1597, Michael Drayton, “Edward the fourth to Shores wife” in Englands Heroicall Epistles, London: N. Ling