Regretfully comes from regretful + -ly. Regret is from Old French regreter ('to bewail, lament'), of uncertain origin, possibly involving a Germanic root related to Old Norse grāta ('to weep'). The historical chain includes Old French regreter. Older glosses in the chain include "to bewail, lament" and "to weep", which help explain the semantic range of the modern word. Morphologically, regretfully is best read as compound, suffixal formation, borrowing, and uncertain formation, yielding an English adverb shaped by both form history and later usage. In current English it functions as an adverb, with the sense "with regret or a feeling of sorrow". related forms include regret, regretful, and regrettable. The result is an English adverb whose etymology preserves the older forms while supporting the word's specialized modern meaning.