As nouns the difference between steroid and ester
is that
steroid is a class of organic compounds having a structure of 17 carbon atoms arranged in four rings; they are lipids, and occur naturally as sterols, bile acids, adrenal and sex hormones, and some vitamins; many drugs are synthetic steroids while
ester is a compound most often formed by the condensation of an alcohol and an acid, with elimination of water. It contains the functional group carbon-oxygen double bond joined via carbon to another oxygen atom.