Subsesqui-

Subsesqui- Sub*ses"qui- [Pref. sub- + sesqui--.] (Chem.) A prefix (also used adjectively) denoting the combination of constituents (especially electro-negative and electro-positive bodies) in the proportion of two to three; as, a subsesqui acetate, i. e., a salt having two equivalents of acetic acid to three of the base. [1913 Webster]