univariant

from The Century Dictionary.

• In mathematics, linearly variant.
• In physical chemistry, having a variance equal to unity. The variance (V) of a chemical system is expressed by the equation V = c + 2 — φ, where c is the number of independent components and φ is the number of phases in which the system may exist.

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

• adjective (Chem.) Having one degree of freedom or variability.

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

• adjective Having a single degree of freedom