Eous

The suffix -eous is an English adjectival ending used to form words that describe qualities, states, or materials. It is not a word by itself but a productive ending that appears in many descriptive terms, especially in scientific and technical vocabulary. Words ending in -eous often convey that something possesses a particular characteristic or composition.

Etymology and formation: The ending comes from Latin -eus, carried into English through Old French and Middle English. In English, -eous is one of several spellings used to render the same Latin idea of “having the nature of.” It typically attaches to a root to yield an adjective, with spelling such that the final form ends in -eous after a wide range of bases.

Representative examples: Aqueous means water-based or consisting of water. Gaseous indicates the properties of a gas or the presence of gas. Igneous describes rocks formed by the cooling and solidification of molten rock. Oleaginous refers to substances that are oily or oil-containing. These examples illustrate how -eous broadly signals a material, state, or characteristic associated with the root.

Usage notes: -eous is common in technical and descriptive language and often appears in contrast to related suffixes such as -ous and -ious. The pronunciation of the ending varies by word, typically realized as a light or syllabic ending like /-iəs/ or /-əs/. While widespread, -eous is not as universally productive as some other suffixes, and not all -eous words share an identical meaning beyond “having the quality of.”