-ous is an English suffix with the following uses.
It is used to create adjectives that describe a quality of the described object derived from the nature of the word the suffix is derived from. For example, "porous surface" means a surface with a special quality: a significant presence of pores. In this function it is similar to the siffedes -en ("wooden"), -ic ("artistic").
In chemistry this suffix has a special function. It is used in chemical nomenclature to name chemical compounds in which a specified chemical element has a lower oxidation number than in the equivalent compound whose name ends in the suffix -ic. See Inorganic nomenclature.