Definition of "burthen"

[...] and thence to Calstock, a town on the Tamar, which is washed by the sea flowing through Plymouth Sound and Hamoaze, and which place vessels of 200 tons burthen can reach at spring tides—[...].

1940 December, Charles E. Lee, “The Wenford Mineral Line”, in Railway Magazine, pages 647, from the Exeter and Plymouth Gazette, October 3, 1834

Nor less, I trust,To them I may have owed another gift,Of aspect more sublime; that blessed mood,In which the burthen of the mystery,In which the heavy and the weary weightOf all this unintelligible world,Is lightened:

1798, William Wordsworth, Lines written a few miles above Tintern Abbey, lines 36–43

It was with a daughter of Mr Shepherd, who had returned, after an unprosperous marriage, to her father's house, with the additional burthen of two children.

1817 (date written), [Jane Austen], Persuasion; published in Northanger Abbey: And Persuasion. […], volumes (please specify |volume=III or IV), London: John Murray, […], 20 December 1817 (indicated as 1818)

In some cases the conquering state contented itself with imposing a tribute on the vanquished: who, being, in consideration of that burthen, freed from the expense and trouble of their own military and naval protection, might enjoy under it a considerable share of economical prosperity, […]

1848, John Stuart Mill, Principles of Political Economy: With Some of Their Applications to Social Philosophy. […], volume I, London: John W[illiam] Parker, […], book I (Production), page 19

Bidding them grope their way out and bestir, […] though the worstBurthen of heat was theirs and the dry thirst

c. 1860, Dante Gabriel Rossetti, The Husbandsmen, lines 4, 6-7

he other men were variously burthened; some carrying picks and shovels – for that had been the very first necessary they brought ashore from the Hispaniola – others laden with pork, bread, and brandy for the midday meal.

1881–1882, Robert Louis Stevenson, Treasure Island, London, Paris: Cassell & Company, published 14 November 1883