specific epithet

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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). Also called trivial name.

Wiktionary

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