In a confusing, bewildering, or extremely irritating manner; used to express frustration.
From confounded + -ly adverbial suffix. Developed as an intensifying adverb in English, often used as a mild oath or expression of exasperation.
Victorian writers loved 'confoundedly'—it's a polite person's way of swearing, a more refined version of stronger curse words, showing how English speakers have always found creative ways to express frustration without being too crude.
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