Pasko

Why the capital, when the months do not get one. Esperanto lowercases a great deal that English capitalises: the days (lundo, vendredo), the languages (esperanto, angla), the adjectives of nationality, and, in modern usage and on this site, the months (januaro, aŭgusto). Feast names go the other way. PMEG is blunt that there are no obligatory capitalisation rules in Esperanto at all, but it treats the feasts as proper names and lists Kristnasko, Pasko, Advento among them, calling the lower-case habit ne imitinda, not worth imitating. So the frequency list carries the lemma as Pasko, this course's Kristnasko page at rank 1033 keeps its capital on the same grounds, and pasko in running text reads as a slip rather than a variant. Ramadano, which arrived later and through a different door, is normally lower case, which tells you the convention is about tradition rather than logic.

What it names. For most speakers Pasko is the Christian Easter, the feast of the resurrection, dated to the first Sunday after the first full moon following the spring equinox and therefore movable between 22 March and 25 April in the Western calendar. The Orthodox churches compute it on the Julian calendar and usually land later. Because the Esperanto word descends from pesaḥ rather than from Easter, it also serves for the Jewish Passover, which is normally distinguished as la juda Pasko or, more precisely, Pesaĥo. Holy Week is la Sankta Semajno, Good Friday Sankta Vendredo, Easter Sunday Paska Dimanĉo.

The vocabulary around it is regular: the adjective is paska, an Easter egg is a paska ovo, and the Easter bunny, a nineteenth-century German import that travelled with the chocolate trade, is the paska leporo. Feliĉan Paskon! is the greeting, in the accusative because you are wishing it upon somebody, the same construction as Feliĉan Kristnaskon!.

For the wider calendar the Esperanto community actually keeps, including the dates that are its own rather than borrowed, see this chapter's article on festivals and the Esperanto calendar.