Definition of posticum in US English:

posticum

noun

Architecture Archaeology
  • A back door or gate; specifically a portico or apartment at the back of an ancient Greek or Roman temple, behind the cella, and corresponding to the pronaos in front.

Origin

Early 18th century; earliest use found in John Harris (c1666–1719), writer and lecturer on science. From classical Latin postīcum back door, rear portico of a temple, use as noun of neuter of postīcus situated at the back, rear.

Pronunciation

posticum

/pɒˈstʌɪkəm/