specific epithet

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

• noun The uncapitalized Latin adjective or noun that follows a capitalized genus name in binomial nomenclature and serves to distinguish a species from others in the same genus, as saccharum in Acer saccharum (sugar maple).

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

• noun taxonomy, botany The second (uncapitalized) word in the scientific name of a species, following the name of the genus.