The story
- Middle English · inherited fromhwenne-so
- English todaywhenso
From Middle English hwenne-so, hwen se, hwense, hwon so, quhen so, wane-so, wen so, weonne so, whanne so, whannse, whan so, whænne-swa, when so, when-so, whon so; equivalent to when + so.
Etymology from Wiktionary, CC BY-SA 4.0.