Burthen meaning : A heavy load. A responsibility, onus. A cause of worry; that which is grievous, wearisome, or oppressive. The capacity of a vessel, or the weight of cargo that she will carry. The tops or heads of stream-work which lie over the stream of tin. The proportion of ore and flux to fuel, in the charge of a blast furnace. A fixed quantity of certain commodities. A birth. The total amount of toxins, parasites, cancer cells, plaque or similar present in an organism. To encumber with a literal or figurative burden. To impose, as a load or burden; to lay or place as a burden (something heavy or objectionable). The tonnage of a ship based on the number of tuns of wine that it could carry in its holds.