four-year-old

the term 'four-year-old' is a modern english compound, a formulaic construction for stating age. its components are deeply ancient: 'four' traces to the proto-indo-european root kʷetwóres, 'year' to yēr-, and 'old' to alt-. while the individual words have millennia of evolution through proto-germanic and old english, their combination into this specific hyphenated pattern is a relatively recent grammatical convention in english. the structure logically and literally denotes the duration of existence, with 'year' serving as the standard unit of measure between the numeral and the state of being 'old'. this transparent compounding reflects english's analytic tendency to create precise modifiers and nouns from simple, foundational vocabulary.

this is a compound adjective/noun formed from three english words joined by hyphens. 'four' is from old english 'fēower', of proto-germanic origin. 'year' is from old english 'gēar', of proto-germanic origin. 'old' is from old english 'eald', of proto-germanic origin. the hyphens link them into a single grammatical unit.