pre-noun adjectival
Used before nouns to describe physical size or scale. Often appears in fixed phrases like 大の字 (spread-eagle shape).
彼は大の字になって寝ている。
He is sleeping spread-eagle.
pre-noun adjectival
grown; adult
Used with nouns like 大人 (adult) or 男 (man) to emphasize full adulthood or maturity.
大の大人がそんなことで泣くな。
Don't cry over something like that, you're a grown adult.
pre-noun adjectival
Expresses strong enthusiasm or a high degree of a personal trait. Common with 好き (liking), ファン (fan), 親友 (close friend), etc.
彼は大の野球ファンだ。
He is a huge baseball fan.
彼女は大の甘党で、毎日ケーキを食べる。
She has a huge sweet tooth and eats cake every day.