The Collaborative International Dictionary
Proemptosis
Proemptosis \Pro`emp*to"sis\, n. [NL., from Gr. ? to fall in before; ? before + ? in + ? to fall.] (Chron.) The addition of a day to the lunar calendar. [R.] See Metemptosis.
Wiktionary
proemptosis
n. The addition of a day to the lunar calendar.