eighteen-year

The compound "eighteen-year" is a modern English construction following a Germanic pattern of number-noun compounding used to specify age or duration. The first element, "eighteen," traces back to Old English 'eahtatēne', literally meaning "eight and ten," a common Germanic method of forming teen numbers. The second element, "year," originates from Proto-Germanic 'jērą', related to cycles and seasons. When combined, the literal meaning "of eighteen years" functions as a single attributive adjective, typically hyphenated when preceding a noun, to denote a specific temporal qualification, most commonly associated with legal age thresholds.

Structure: eighteen (number) + year (time period) - eighteen: From Old English 'eahtatēne', a compound of 'eahta' (eight) and 'tēne' (ten). It functions as the cardinal number in this compound adjective. - year: From Old English 'gēar', meaning a period of twelve months. It functions as the unit of time measurement in this compound adjective.