matstsah (Hebrew #4682)
properly, sweetness; concretely, sweet (i.e. not soured or bittered with yeast); specifically, an unfermented cake or loaf, or (elliptically) the festival of Passover (because no leaven was then used)
KJV usage: unleaved (bread, cake), without leaven.
Pronounce: mats-tsaw'
Origin: from 4711 in the sense of greedily devouring for sweetness