The Collaborative International Dictionary of English v.0.48:

matzo \matz"o\, matzoh \matz"oh\, n.; pl. E. matzos or
   matzohs; Hebr. matzoth [Heb. matsts[=o]th, pl. of
   matsts[=a]h unleavened.]
   A cake of unleavened bread eaten by the Jews at the feast of
   the Passover.
   [1913 Webster]

WordNet (r) 3.0 (2006):

matzo
    n 1: brittle flat bread eaten at Passover [syn: matzo,
         matzoh, matzah, unleavened bread]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "matzo":
   Agnus Dei, French bread, Holy Grail, Host, Irish soda bread,
   Italian bread, Pieta, Sanctus bell, Sangraal, ark, asperger,
   asperges, aspergillum, bambino, beadroll, beads, black bread,
   bread, bread stick, bread stuff, brown bread, candle, censer,
   chaplet, ciborium, cracked-wheat bread, cross, crucifix, cruet,
   crust, dark bread, eucharistial, garlic bread, graham bread,
   holy cross, holy water, holy-water sprinkler, icon, incensory,
   loaf of bread, matzoth, menorah, mezuzah, mikvah, monstrance,
   nut bread, osculatory, ostensorium, pain, paschal candle, pax,
   phylacteries, pita, prayer shawl, prayer wheel, pumpernickel, pyx,
   raisin bread, relics, rood, rosary, rye bread, sacramental,
   sacred relics, sacring bell, salt-rising bread, shofar, sourbread,
   sourdough bread, staff of life, sukkah, tabernacle, tallith,
   thurible, toast, tommy, unleavened bread, urceole, veronica,
   vigil light, votive candle, white bread, whole wheat bread