Category:English singularia tantum

Definition from Wiktionary, a free dictionary

See also: Category:English pluralia tantum

Singularia tantum are nouns which have no plural form but are not grammatically uncountable.

Note that this usage is non-standard – other usages specifically include and emphasize uncountable/non-count nouns:

Shorter Oxford English Dictionary as: "Gram. A word having only a singular form; esp. a non-count noun." (The New Shorter Oxford English Dictionary, 1993 edition, p. 2871.)