dichromic acid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An acid, H₂Cr₂O₇, found only in solution.

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

• noun inorganic chemistry A relatively unstable form of chromic acid, H2Cr2O7, known only in solution or as its salts, the dichromates, from which it may be prepared.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the hypothetical acid (H2Cr2O7) from which dichromates are derived; known only in solution and in the form of dichromate salts