Batseq means to swell or swell up, particularly referring to dough that rises through the action of leaven. The verb describes the fermentation process that causes bread dough to expand and become puffy. It is closely related to the noun batseq (H1217), meaning "dough."
The swelling of dough is theologically significant because of the central role of leaven in Israel's liturgical calendar. At Passover, Israel was commanded to eat unleavened bread — bread that had not been allowed to batseq (swell). The haste of the Exodus left no time for dough to rise (Exodus 12:34, 39). This became an annual reminder that salvation comes suddenly, leaving no room for human preparation. Hosea uses the image of dough swelling with leaven to picture the slow, hidden corruption of Israel's idolatry (Hosea 7:4).