The Collaborative International Dictionary
Velarium \Ve*la"ri*um\, n.; pl. Velaria. [L., a covering.] (Zo["o]l.) The marginal membrane of certain medus[ae] belonging to the Discophora.
Wiktionary
n. 1 (cx zoology English) The marginal membrane of certain medusae belonging to the Discophora. 2 (cx historical English) An awning that stretched over the seating area of the Colosseum in Ancient Rome.
Wikipedia
A velarium ("curtain") was a type of awning used in Roman times. It stretched over the whole of the cavea, the seating area in the Colosseum, to protect spectators from the elements. Precisely how the awning was supported is a matter of conjecture.
The velarium that covered the Colosseum in Rome provided both shade and slight protection from rain, although the main use of the velarium was to create a ventilation updraft, creating circulation and a cool breeze.
Usage examples of "velarium".
In despair, and in a terror which beat down even pride, he glanced his eyes over the rolling and rushing crowd—when, right above them, through the wide chasm which had been left in the velaria, he beheld a strange and awful apparition—he beheld—and his craft restored his courage!
The pile extended the width of the Circus, and was flanked on both sides by towers which, besides helping the architects give grace to their work, served the velaria, or purple awnings, stretched between them so as to throw the whole quarter in a shade that became exceedingly grateful as the day advanced.
Where, the huge velarium that Nero had stretched across the Colosseum at Rome, that Titan sail of purple on which was represented the starry sky, and Apollo driving a chariot drawn by white gilt-reined steeds?
Where the huge velarium that Nero had stretched across the Colosseum at Rome, that Titan sail of purple on which was represented the starry sky, and Apollo driving a chariot drawn by white, gilt-reined steeds?