The story
- Old English · inherited fromġemynd
- Medieval Latin · derived fromdies mensis“day of the month”
- Middle English · inherited frommonethes mynde
- English todaymonth's mind
From Middle English monethes mynde under influence from Medieval Latin dies mensis (“day of the month”) and Old English ġemynd, whose principal sense was "memory".
Etymology from Wiktionary, CC BY-SA 4.0.