In linguistics, a measure word is a word used to denote the quantity of a particular noun. Measure words are applied to nouns which are not countable. In some cases, a measure word may be a specific unit of measurement. For instance, in the phrase "five tons of flax," "tons" is a measure word.
In English, not all nouns require measure words in order to denote quantity. For example, it is possible to say "five people" without having to specify a measure word. These nouns are said to be countable — that is, each noun indicates a discrete unit. Nouns of this type are also known as "count nouns".
By contrast, other nouns are known as mass nouns. A mass noun indicates something which is continuous rather than discrete. For instance, "milk" is a mass noun because there is no inherent discrete division in milk. The contrast between a count and a mass noun is visible in the phrase "three cookies and three glasses of milk." "Cookies," a countable noun, does not require a measure word, while "milk," a mass noun, requires the measure word "glasses."
This distinction between countable and uncountable nouns varies slightly from language to language. In some languages, even countable nouns require another word to be added when a number of that noun is being described. This type of word is called a numeral classifier. Some speakers also use the term "measure word" to describe this type of classifier. In fact, although there are many similarities between numeral classifiers and measure words, they are slightly different in important ways.
Numeral classifiers occur frequently in some languages, but not in others. For example, all forms of Chinese make extensive use of numeral classifiers. It is very difficult to translate these words into English, because they have no precise grammatical equivalent. For instance, in Mandarin Chinese, the phrase "one person" contains three words: the word for "one," the word for "person," and the numeral classifier for people, a word which has no direct English translation. Mandarin has over one hundred such classifiers.
Many sources refer to this type of numeral classifier as a measure word, and the two types of word are similar in some ways. The primary difference is that numeral classifiers apply to countable nouns. Their grammatical function is different from that of measure words; measure words make uncountable nouns countable, while numeral classifiers are required for count nouns to be counted.