-acioussuffix
Primary stress is attracted to the first syllable of this suffix and vowels may be reduced accordingly; see e.g.
perspicacious adj.Origin: A borrowing from Latin, combined with an English element. Etymons: Latin -āci- , -āx , -ous suffix.
Etymology: < classical Latin -āci-, -āx, adjective ending added chiefly to verb stems + -ous suffix. Compare French -ace , Spanish -az , Italian -ace . Compare -acy suffix 1 and -acity suffix.English adjectives in -acious from Latin adjectives in -āx are found from the first half of the 16th cent. (e.g. efficacious adj.; also earlier fallacious adj. from the corresponding Latin noun). Formations on different types of stems are found from the second half of the 16th cent. (see carpacious adj., palacious adj.). In some cases adjectives in -acious are formed on Latin verbs in -āre (where no Latin adjective in -āx is attested), e.g. indagacious adj., volacious adj., predacious adj. (all 17th cent.). Adjectives are also formed on Latin verbs of other conjugations, e.g. scribacious adj. (also 17th cent.). Some adjectives in -acious are derived < Latin adjectives in -ācus , e.g. meracious adj., opacious adj. (both 17th cent.). The 19th cent. gave rise to a number of ad hoc formations, e.g. gesticulacious adj., newspaperacious adj. at newspaper n. Derivatives, and quizzacious adj.
This entry has been updated (OED Third Edition, September 2009; most recently modified version published online March 2021).