burthen

1. A heavy load.
2. A responsibility, onus.
3. A cause of worry; that which is grievous, wearisome, or oppressive.
4. The capacity of a vessel, or the weight of cargo that she will carry.

   a ship of a hundred tons burden

5. The tops or heads of stream-work which lie over the stream of tin.
6. The proportion of ore and flux to fuel, in the charge of a blast furnace.
7. A fixed quantity of certain commodities.

   A burden of gad steel is 120 pounds.

8. A birth.
9. The total amount of toxins, parasites, cancer cells, plaque or similar present in an organism.

1. To encumber with a literal or figurative burden.

   to burden a nation with taxes

2. To impose, as a load or burden; to lay or place as a burden (something heavy or objectionable).

noun

The tonnage of a ship based on the number of tuns of wine that it could carry in its holds.