This feature is a morphological one, and not a semantic one. Most of the (common) nouns vary according to the number; it exists nevertheless a range of nouns that have only a singular form (for example le sud), or that have only a plural form (les fiançailles). Some nouns have the same graphical form in singular and plural:
The signification of a noun can change according to the number (for example le travail, les travaux).