Sentence:  <WSD>Epicene</WSD> nouns are equally misunderstood: they are of one gender only. These, like the common, represent under one word each member of a pair of animals—the male and the female: thus "passer"—a sparrow—denotes the cock sparrow, as well as the hen: but in the use of these words there is no variation of the gender: they are invariably used in one gender only: thus "passer" is of the masculine gender: and though used for the purpose of representing the hen-sparrow; still every adjective or participle connected with it must be used in the masculine gender: [...] In short, <WSD>epicene</WSD> nouns differ from the common in this only; that they do not vary their genders in accordance with nature: they invariably keep to one gender. 
Meaning of the word marked with <WSD> tags:  Of or relating to a class of Greek and Latin nouns that may refer to males or females but have a fixed grammatical gender (feminine, masculine, neuter, etc.).