yearday

• year-day, year day, year's day

From Middle English ȝereday, ȝerdai (“anniversary”), from Old English *ġēardæġ (found in plural ġēardagas (“days of yore”)), from Proto-West Germanic *jāradag (“anniversary day”), equivalent to year +‎ day. Cognate with West Frisian jierdei (“birthday”), Dutch jaardag (“birthday”), German Jahrtag (“anniversary”).

yearday (plural yeardays)

1. Synonym of anniversary, a day occurring in a yearly cycle, particularly
   • 1887, Michael Baxter, Forty coming wonders:

     The Second Advent of Christ to remove to heaven his waiting people takes place at the end of the yearday sixth vial in accordance with his personal announcement, [...]

   • 1998, Australian Journal of Botany, volume 46:

     [...] the amended yearday which was the middle day in flowering range. the yearday which is equivalent to commencement of flowering. the amended yearday (based on flowering yearday) which is the equivalent to the commencement of [...]

   1. (dated) Synonym of deathday or (Christianity) year's mind, the anniversary of a person's death, particularly as observed with a requiem mass or other commemoration.
      • 1907, William Page, The Victoria history of the county of Suffolk, volume 1, page 660:

        His executors were to keep his yearday for twenty years at the cost of 20s. per year, and finally after his wife's death the bailiffs and commonalty of Southwold were to find a priest for sixteen years next following to sing for his soul […]

      • 1998, Plutarch (in translation), Lives of the Noble Grecians and Romans, page 310:

        For they were the very days on the which the women celebrated the feast and yearday of Adonis' death: and there were also in divers parts of the city, images of dead men carried to burial, and women following them, mourning and lamenting.

      • 2009, Georgette Heyer, My Lord John: A tale of intrigue, honor and the rise of a king, page 56:

        The younger children remained at Bytham for a year, and saw their brothers again only at Leicester, on the yearday of Mother's death.

2. (mathematics) Synonym of day in relation to idealized computations of the year.
   • 1985, Mathematics magazine, volume 58:

     To avoid the idiosyncracies^[sic] of leap years, we propose, as a first approximation to the actual yearday, a standardized yearday s that is a function of ( m, d) only, s = S(m) +dl (6) where 5 is a function of m only.

   • 2000, Agricultural and forest meteorology;, volumes 104-105:

     ... T₁max the maximum (cloud-free) daily total transmittance at a location with a given elevation and near-surface water-vapor pressure on a given yearday, [...]

   • 2002, Journal of physical oceanography, volume 32:

     Its power supply failed at yearday 227 (0300), [...]