In linguistics, singulative number and collective number (abbreviated SGV and COL) are terms used when the grammatical number for multiple items is the unmarked form of a noun, and the noun is specially marked to indicate a single item. When a language using a collective-singulative system does mark plural number overtly, that form is called the plurative.

This is the opposite of the more common singular–plural pattern, where a noun is unmarked when it represents one item, and is marked to represent more than one item. "Collective number" should not be confused with collective nouns.

Welsh has two systems of grammatical number, singular–plural and collective–singulative. Plurals are unpredictable and formed in several ways: by adding a suffix to the end of the word (usually -au), as in tad and tadau, through vowel mutation, as in bachgen and bechgyn, or through a combination of the two, as in chwaer and chwiorydd. Other nouns take the singulative suffixes -yn (for masculine nouns) or -en (for feminine nouns). Most nouns which inflect according to this system designate objects that are frequently found in groups, for example adar "birds/flock of birds", aderyn "bird"; mefus "a bed of strawberries", mefusen "a strawberry"; plant "children", plentyn "a child"; and coed "forest", coeden "a tree". Still other nouns suffixes for both singular and plural forms (e.g. merlen "pony", merlod "ponies"); these are similar to nouns formed from other categories of words (e.g. cardod "charity" gives rise to cardotyn "beggar" and cardotwyr "beggars").