Illustrated Companion to the Latin Dictionary/Opa

This article incorporates text from a publication now in the public domain: Rich, Anthony (1849). The illustrated companion to the Latin dictionary, and Greek lexicon. p. vi. OCLC 894670115. https://archive.org/details/illustratedcompa00rich. 

OP'A or OP'E (ὀπή). A Greek term, for which the Roman architects employed the word columbarium. (Vitruv. iv. 2. 4.) It signifies the bed or cavity in which the head of a tie-beam (tignum) rests; whence the space between one opa or tignum and another was termed metopa or intertignium.