Single opening with multiple doors: "trapdoor" or "trapdoors"

Is it "a trapdoor" or "trapdoors" for one opening with two or more doors covering it? One example is the one(s) covering Black Horse Inn’s cellar.

Clearly it is plural when there are two or more separate openings each covered by one or more doors, and it is singular when there is one opening covered by one door. Cambridge Dictionary says a trapdoor is "a small door in a ceiling or floor", and Merriam Webster and Oxford similarly describe a single door covering a single opening. The title on the Black Horse Inn Cellar example image refers to a "trap door", which is singular but also an open compound word rather than a closed compound word.

I cannot find an official reference disambiguating this, so perhaps either way is correct?