1] the paschal sacrifice (which was accustomed to be offered for the people's deliverance of old from Egypt)
2] the paschal lamb, i.e. the lamb the Israelites were accustomed to slay and eat on the fourteenth day of the month of Nisan (the first month of their year) in memory of the day on which their fathers, preparing to depart from Egypt, were bidden by God to slay and eat a lamb, and to sprinkle their door posts with its blood, that the destroying angel, seeing the blood, might pass over their dwellings; Christ crucified is likened to the slain paschal lamb
3] the paschal supper
4] the paschal feast, the feast of the Passover, extending from the 14th to the 20th day of the month Nisan
derivation: of Aramaic origin cf (06453)
http://bible.crosswalk.com/Lexicons/Greek/grk.cgi?number=3957&version=kjv

(06453)
1] passover
   1.a] sacrifice of passover
   1.b] animal victim of the passover
   1.c] festival of the passover
derivation: from (06452)
http://bible.crosswalk.com/Lexicons/Hebrew/heb.cgi?number=6453&version=kjv

(06452)
1] to pass over, spring over
   1.a] (Qal) to pass over
   1.b] (Piel) to skip, pass over
2] to limp
   2.a] (Qal) to limp
   2.b] (Niphal) to be lame
   2.c] (Piel) to limp
derivation: a primitive root
http://bible.crosswalk.com/Lexicons/Hebrew/heb.cgi?number=6452&version=kjv

Additional information:
http://www.cswnet.com/~duxrow/webdoc22.htm
asserts that "the three great feasts" were the Passover, Pentecost (Harvest), and Tabernacles.