2.247 numbers in compound adjectives

Cardinal numbers can be used as part of a compound adjective, (see paragraphs 2.98 to 2.107). The cardinal number is used in front of a noun to form a compound adjective which is usually hyphenated

Note that the noun remains singular even when the number is two or more, and that compound adjectives which are formed like this cannot be used as complements. For example, you cannot say 'My essay is five-hundred-word'. Instead you would probably say 'My essay is five hundred words long'.