a substance capable of bringing about fermentation(noun.substance)
source: wordnet30
a process in which an agent causes an organic substance to break down into simpler substances; especially, the anaerobic breakdown of sugar into alcohol(noun.process)
To cause ferment of fermentation in; to set in motion; to excite internal emotion in; to heat.(verb)
source: webster1913
To undergo fermentation; to be in motion, or to be excited into sensible internal motion, as the constituent particles of an animal or vegetable fluid; to work; to effervesce.(verb)