Merriam-Webster's Collegiate® Dictionary, 11th Edition
FERMENT
I. verb
Date: 14th century
intransitive verb to undergo fermentation, to be in a state of agitation or intense activity, transitive verb to cause to undergo fermentation, to work up (as into a state of agitation) ; foment , fermentable adjective
II. noun see: barm
Date: 15th century
1. a living organism (as a yeast) that causes fermentation by virtue of its enzymes, enzyme ,
2. a state of unrest ; agitation, a process of active often disorderly development