popularly called Sunday-letter, one of the seven letters A B C D E F G, used in almanacks, ephemerides, &c. to denote the Sundays throughout the year. See Astronomy, n° 310. The word is formed from *dominica* or *dominicus dies*, Lord's-day, Sunday.

The dominical letters were introduced into the calendar by the primitive Christians, in lieu of the nundinal letters in the Roman calendar.