hexabasic

from The Century Dictionary.

• Having a basicity of six; capable of combining with a proportion of base or metal equivalent to six atoms of hydrogen.

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

• adjective (Chem.) Having six hydrogen atoms or six radicals capable of being replaced or saturated by bases; -- said of acids.

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

• adjective chemistry, of an acid containing six replaceable hydrogen atoms
• adjective chemistry having six atoms of a univalent metal