闰余
岁首月龄

Epact \E"pact\ ([=e]"p[a^]kt), n. [F. ['e]pacte, fr. Gr.
'epakto`s brought on or in, added, fr. 'epa`gein to bring on
or in; 'epi` on, in + 'a`gein to bring or lead. See {Epi-},
and {Act}.] (Chron.)
The moon's age at the beginning of the calendar year, or the
number of days by which the last new moon has preceded the
beginning of the year.

{Annual epact}, the excess of the solar year over the lunar
year, -- being eleven days.

{Menstrual epact}, or {Monthly epact}, the excess of a
calendar month over a lunar.