foris

Foris, foris is third declension feminine, and in practice a plural word: fores are the two leaves of a Roman double door, so the plural is the default even for one doorway. Distinguish the vocabulary carefully. Porta is the gate of a city or a camp, ianua is the front door of a house, ostium is the opening itself, limen is the threshold, and fores are the panels that swing.

The trap is homonymy, and it is a nasty one. Foris is also an adverb meaning "outside, out of doors", with a companion foras, "to the outside", and both are extremely common. So a bare foris in a text may be a noun in the nominative or genitive singular or an adverb, and only the syntax decides. Add to that forem, which is an old imperfect subjunctive of sum as well as an accusative of this noun.