• (a.) Capable of uniting with five molecules of a monacid base; having five acid hydrogen atoms capable of substitution by a basic radical; -- said of certain acids.
Pen`ta·ba'sic adjective [ Penta- + basic .] (Chemistry) Capable of uniting with five molecules of a monacid base; having five acid hydrogen atoms capable of substitution by a basic radical; -- said of certain acids. 
Type: Term Pronunciation: pen′tă-bā′sik Definitions: 1. Denoting an acid having five replaceable hydrogen atoms.