To be leavened, to become sour or fermented. This root underlies the entire biblical theology of leaven. During Passover, Israel was commanded to remove all chamets (leavened bread) from their homes — a practice still observed today. The word also metaphorically means to be embittered or oppressive.
Chamets became one of Scripture's most powerful symbols. Leaven represents the pervasive spread of sin — a little works through the whole batch (Galatians 5:9). The Passover prohibition against chamets pointed to the need for spiritual purity. Jesus warned of the 'leaven of the Pharisees' (hypocrisy), and Paul urged believers to celebrate the feast 'without the old leaven' of malice and wickedness (1 Corinthians 5:8).