I know that there is no Classical concept of work in contrast with life (as in "I was at work yesterday" or "At work, people did X", etc.), but I was wondering if there is any post-Classical Latin word that fills that gap (be it in Medieval, Ecclesiastical, New Latin or Contemporary Latin). Does anybody know of something of the sort? Thank you in advance!
The most suitable words seem to be negotium, opera (feminine), opus (neuter, plural opera), and labor. All are classical words that can be used for that purpose, but work in the sense you describe appears not to have been a set concept in the ancient world. Different situations might call for different words, but the best general match in the setting you describe is negotium in my opinion.
This also has the benefit that it contrasts with otium, which you could translate as "free time". So work, neg-otium, is "not free time".