The phrase "一大早" (yīdàzǎo) is formed through a common Chinese collocation pattern where the numeral "一" (yī, one) intensifies the adjective "大" (dà, big), which in turn modifies the core noun "早" (zǎo, morning/early). Literally meaning "one big early", it functions as an idiomatic adverbial phrase where "一大" acts as a vivid, exaggerated modifier for "早", collectively conveying the meaning of "very early in the morning" with a stronger, more colloquial emphasis than simply saying "早晨" (zǎochen, morning).