The word "前脚" is formed by directly combining the character "前", meaning "front" or "before", with the character "脚", meaning "foot", resulting in a literal meaning of "front foot". This compound is used primarily in temporal expressions to denote an action that occurs immediately before another, as seen in constructions like "前脚走，后脚到", where it functions to sequence events closely in time. The formation relies on the semantic contribution of each character, with "前" modifying "脚" to convey a sense of precedence or position.