Source : Webster's Revised Unabridged Dictionary (1913)

Propylaeum \Prop`y*l[ae]"um\, n.; pl. {Propyl[ae]a}. [L., fr.
   Gr. ?; ? before + ? a gate.] (Anc. Classical Arch.)
   Any court or vestibule before a building or leading into any
   inclosure.