forum

Forum, fori is second declension neuter, and it started as the open space outside - the same root as fores and foras - before it meant anything civic. Then it was the market square, and then the particular square at Rome where courts, politics and banking all happened at once.

Because of that, forum on its own frequently means "the law courts": in foro versari is to practise as an advocate, and forum agere is to hold assizes. Rome exported the word as a place name across the empire, which is why Forum Iulii is now Frejus and Forum Livii is Forli. English kept forum unchanged and, from the legal sense, forensic - which is why forensic science is strictly science for the courtroom, not science about corpses.