This word is not acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. In Greco-Rom. archæol., the front door or the vestibule or porch of entrance to any building.

"The first of these names is derived from the mosaic pavement in the prothyrum, in which the objects mentioned are represented; while a medallion picture in the atrium, with heads of"