Affixes

In the same way that many Latin words ending in ‑us arrived in English through French with the ending changed to ‑ous, some of those in ‑arius changed to ‑arious (others took on the endings ‑arian or ‑ary² instead).

Words in ‑arious are adjectives. Some common examples are gregarious (Latin greg‑, grex, a flock or herd), fond of company or sociable; precarious (Latin prex, prec‑, prayer), uncertain or insecure; nefarious (Latin nefas, nefar‑, wrong), wicked or criminal; vicarious (Latin vicarius, substitute), of something experienced through the feelings or actions of another person; and various (Latin varius, changing or diverse).

This suffix has never been active in English; examples that appear to exist have actually been formed by attaching ‑ous (or its variant ‑ious) to a word stem containing ‑ar‑: burglarious, hilarious, uproarious.