singulare tantum
Definition - A noun that is only used as in its singular form.

1. As opposed to a plurale tantum, which is a noun that is only used in its plural form (e.g. suds).

Example -
dust and wealth

Etymology -
In Latin the phrase means "singular only."

Oxford English Dictionary -
Its first citation is from 1940:
"A singulare tantum has developed a plural by cutting the designated entity, like a worm, into two parts."
( A. H. Gardiner, Theory of Proper Names, pg. 27)

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