Ses'qui-

. [Lat., one half more, one and a half.] (Chem.) A prefix denoting the proportion of three equivalents of the substance to the name of which it is prefixed to two equivalents of the other element, or proximate principle; as, sesquioxide. Sesquioxide is sometimes used in the same manner to denote the proportions of two and a half to one, or rather of five to two.