-eoussuffix

Occurring in adjectives, is chiefly < Latin -e-us + -ous suffix. The English words with this suffix are for the most part practically mere adaptations of Latin adjectives in -eus, the senses of which they generally retain. While, however, the Latin adjectives in -eus < nouns denoting material substances have usually the sense ‘composed of’, as well as the sense ‘of the nature of, resembling’, their English derivatives in -eous express the latter meaning only: compare, e.g. argenteous, ligneous, vitreous, with the corresponding words in Latin. In a very few cases (e.g. aqueous) English adjectives in -eous have been formed directly on Latin nouns. The Latin ending -eus also occurs as part of a compound suffix, as in the words in -āceus (see -aceous suffix) and -āneus (cf. consentaneous adj., instantaneous adj.).

2. In beauteous, bounteous, duteous, plenteous, the ending -eous arises from the addition of the suffix -ous to -te, earlier form of -ty suffix¹; but in the older words of this formation -teous replaces an earlier -tivous, < French -tif + -ous suffix; e.g. bounteous was originally bountivous, < French bontif, < bonté: see bounty n.

3. In a few instances -eous is an analogical deformation of other suffixes, as in righteous (for rightwise), courteous, for Middle English curteis < Old French curteis (-eis:—Latin -ēnsem).