The story
- Proto-Germanic · inherited from*seldalīkaz
- Proto-West Germanic · inherited from*seldalīk
- Old English · inherited fromsellīċ
- Middle English · inherited fromselly
- English todayselly
From Middle English selly, selly, sellich, from Old English sellīċ, seldlīċ (“rare, strange, wondrous”), from Proto-West Germanic *seldalīk, from Proto-Germanic *seldalīkaz, equivalent to seld + -ly. Cognate with Scots selly, silly (“approved, good, worthy”), Old Saxon seldlīk (“rare, wonderful”), Gothic 𐍃𐌹𐌻𐌳𐌰𐌻𐌴𐌹𐌺𐍃 (sildaleiks, “wonderful”).
Etymology from Wiktionary, CC BY-SA 4.0.