Onus

·noun A burden; an Obligation.

onus
ŏnus (in good MSS. also wr. hŏnus), ĕris, n. [etym. dub.; cf. Sanscr. anas, a wagon for freight], ...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
onus
onus eris, n AN-, a load, burden : tanta onera navium, ships of so great burden , Cs.: clipei ing...

An Elementary Latin Dictionary