negotium

Negotium, negotii, n., second declension, and its etymology is the definition: nec plus otium, "not leisure". Otium is the free time a Roman gentleman spends on reading, philosophy and his estate; negotium is everything that eats into it. So the word means business, a task, an affair, and by an easy slide the trouble the task causes - which is why sine negotio means "easily" and magno negotio means "with great difficulty".

The corpus writes negocio as often as negotio. That is a medieval spelling following a medieval pronunciation, not a separate word, and it should not be treated as one. Italian negozio is still a shop; English took negotiate and negotiable, both of which have kept the busy half and lost the tiresome one.