pentacid

from The Century Dictionary.

• Noting a base containing five combining units of the radical hydroxyl, HO, or one equivalent to a pentabasic acid, molecule for molecule.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Chem.) Capable of neutralizing, or combining with, five molecules of a monobasic acid; having five hydrogen atoms capable of substitution by acid residues; -- said of certain complex bases.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective chemistry Capable of neutralizing, or combining with, five molecules of a monobasic acid; having five hydrogen atoms capable of substitution by acid residues; said of certain complex bases.