Partitive plural is a grammatical number

Grammatical number

In linguistics, grammatical number is a grammatical category of nouns, pronouns, and adjective and verb agreement that expresses count distinctions ....

 that is used to modify a noun which represents a part of some whole amount, as opposed to the comprehensive plural, used when the noun represents the total amount of something. This plural form is used in the Finnish language

Finnish language

Finnish is the language spoken by the majority of the population in Finland Primarily for use by restaurant menus and by ethnic Finns outside Finland. It is one of the two official languages of Finland and an official minority language in Sweden. In Sweden, both standard Finnish and Meänkieli, a...

, and its use in this language influenced J.R.R. Tolkien in inventing his fictional language

Constructed language

A planned or constructed language—known colloquially as a conlang—is a language whose phonology, grammar, and/or vocabulary has been consciously devised by an individual or group, instead of having evolved naturally...

 Quenya

Quenya

Quenya is a fictional language devised by J. R. R. Tolkien, and used in his Secondary world, often called Middle-earth.Quenya is one of the many Elvish languages spoken by the immortal Elves, called Quendi in Quenya. The tongue actually called Quenya was in origin the speech of two clans of Elves...

. It refers to more than one object that is nevertheless only part of a larger number; for example, three out of four of something. It is one of four grammatical numbers in Quenya, the others being singular, dual

Dual (grammatical number)

Dual is a grammatical number that some languages use in addition to singular and plural. When a noun or pronoun appears in dual form, it is interpreted as referring to precisely two of the entities identified by the noun or pronoun...

, and plural

Plural

In linguistics, plurality or [a] plural is a concept of quantity representing a value of more-than-one. Typically applied to nouns, a plural word or marker is used to distinguish a value other than the default quantity of a noun, which is typically one...

.

As for the Finnish partitive

Partitive case

The partitive case is a grammatical case which denotes "partialness", "without result", or "without specific identity". It is also used in contexts where a subgroup is selected from a larger group, or with numbers....

 plural, it is really a regular case

Grammatical case

In grammar, the case of a noun or pronoun is an inflectional form that indicates its grammatical function in a phrase, clause, or sentence. For example, a pronoun may play the role of subject , of direct object , or of possessor...

 form in the plural number

Grammatical number

In linguistics, grammatical number is a grammatical category of nouns, pronouns, and adjective and verb agreement that expresses count distinctions ....

, but which is used in the singular as well, denoting an abstract, unknown identity or result.