FROM STRONG’S HEBREW DICTIONARY (1890)

Strong’s Hebrew Dictionary (1890) — public domain, printed whole.

matstsah mats-tsaw' — from 4711 in the sense of greedily devouring for sweetness; 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):--unleaved (bread, cake), without leaven.

see HEBREW for 04711