noun

1. a substance or organism causing fermentation, as yeast, bacteria, enzymes, etc.
2. fermentation
3. a state of excitement or agitation

Etymology: ME < OFr < L fermentum, leaven, yeast < fervere, to boil, be agitated: see barm

transitive verb

1. to cause fermentation in
2. to excite; agitate

intransitive verb

1. to be in the process of fermentation
2. to be excited or agitated; seethe