propylaeum
noun
pro·py·lae·um ˌprä-pə-ˈlē-əm 
ˌprō-
plural propylaea ˌprä-pə-ˈlē-ə
ˌprō-
: a vestibule or entrance of architectural importance before a building or enclosure —often used in plural
Word History
Etymology
Latin, from Greek propylaion, from pro- before + pylē gate — more at pro-
First Known Use
1637, in the meaning defined above