a crystalline plant sterol, CHOH, formerly prepared from ergot but now chiefly from yeast: when exposed to ultraviolet rays it produces a vitamin (D) used to prevent or cure rickets
Origin:
< ergot + sterol
See ergosterol in American Heritage Dictionary 4
noun
A crystalline sterol, C28H43OH, synthesized by yeast from sugars or derived from ergot and converted to vitamin D2 when exposed to ultraviolet radiation.