noun

• (mining) The tops or heads of stream-work which lie over the stream of tin.
• (metalworking) The proportion of ore and flux to fuel, in the charge of a blast furnace.
• (obsolete, rare) A birth.
  "… that bore thee at a burden two fair sons."
• (medicine) The total amount of toxins, parasites, cancer cells, plaque or similar present in an organism.

verb

• (transitive) To encumber with a literal or figurative burden.
  "to burden a nation with taxes"
• (transitive) To impose, as a load or burden; to lay or place as a burden (something heavy or objectionable).

noun

• (music) A phrase or theme that recurs at the end of each verse in a folk song or ballad.
  "Foot it featly here and there; / And, sweet sprites, the burden bear."