The interjection "哇塞" (wā sāi) is formed through a process of phonetic borrowing and semantic shift originating from the Min Nan dialect, where its original form expressed a vulgar exclamation. In its adoption into mainstream Mandarin, the two characters were chosen primarily for their sound to approximate the dialectal expression, with "哇" (wā) being a common onomatopoeia for amazement (like "wow") and "塞" (sāi) serving as a phonetic component. Over time, the offensive connotation was entirely stripped away, and the fused pair evolved into a fixed, lively colloquial term used exclusively to convey surprise, admiration, or excitement, with its constituent characters losing their individual literal meanings ("stuff" or "plug" for 塞) in this specific exclamatory context.