What is onus in Latin?

Excuse me, could you possibly enlighten me on the meaning of the term "onus" in the Latin language? I'm quite intrigued by its etymology and how it has evolved through time, particularly in the context of legal or philosophical discussions. I'm hoping that you might have some insight into its origins and the nuances it carries within the Latin lexicon. Your expertise in the field of linguistics would be invaluable in shedding light on this intriguing topic.