seventy-eight-year-old

the term is a modern english compound, directly constructed from its constituent numerical and descriptive elements. "seventy" derives from old english "hundseofontig", meaning "seven tens", while "eight" comes from old english "eahta". the pattern of combining a tens digit and a unit digit with a hyphen follows standard english numerical convention. the hyphenated phrase "year-old" is a productive pattern in english for forming compound adjectives and nouns indicating age, originating from the old english words "gear" (year) and "eald" (old). the entire compound functions as a single lexical unit to precisely denote a specific age.

this is a compound adjective/noun formed by combining the cardinal number "seventy-eight" with the hyphenated phrase "year-old". it is not segmentable into classical morphemes as it is a modern english numerical construction.