burthen

noun4

1. •
   Rarely used musical tempo, meaning slow and ponderous (e.g., moving under a burden); similar to largo.
2. •
   A section of music with the tempo mark burthen.
3. •
   (no longer used) Archaic form of burden.

   • 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
4. •
   (no longer used, historical) The tonnage of a ship based on the number of tuns of wine that it could carry in its holds.

   • It was a vessel of about seventy tons burthen, and shaped something like a Chinese junk. — 1869