[tengwar2]

An ossuary is usually something like a building (e.g. a charnel house), but apparently you are right in saying that it is applied to Jewish bone-boxes (https://en.wikipedia.org/wiki/Ossuary#Jewish_ossuaries). For the other meaning, they can be vast. I visited the Paris Catacombs (https://en.wikipedia.org/wiki/Catacombs_of_Paris) and estimated that the remains of about 3M people were down there.