butyric : Idioms & Phrases

• noun an unpleasant smelling fatty acid found especially in butter
  butanoic acid.
  

WordNet

• C3H7.CO2H, an acid found in butter; an oily, limpid fluid, having the smell of rancid butter, and an acrid taste, with a sweetish aftertaste, like that of ether. There are two metameric butyric acids, called in distinction the normal- and iso-butyric acid. The normal butyric acid is the one common in rancid butter.

Webster 1913