E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
O.
The fifteen Os are fifteen prayers beginning with the letter O (See Horæ Beatissimæ Virginis Mariæ.)
1
The Christmas Os. For nine days before Christmas (at 7 oclock p,m.) are seven antiphones (3 syl.), each beginning with O, as O Sapientia, O Radx, etc.