Where does “fickle mistress” come from?

fickle mistress (English) comes from English Mistress, from Middle English maistresse, from Old French maistresse, from Old French maistre, from Latin magister, from Proto-Italic magisteros, from Proto-Indo-European méǵh₂isteros, from Proto-Indo-European méǵh₂s — big, great.

Ancestry of “fickle mistress”, step by step

fickle mistress traces back through two separate lines of ancestry.

via English Mistress

StepLanguageWordMeaning
1EnglishMistressUsed as the title of a married woman before her...
2Middle Englishmaistressemistress
3Old Frenchmaistresse
4Old Frenchmaistremaster; Master; magister
5Latinmagisterteacher; master; a title of the Middle Ages,...
6Proto-Italicmagisterosbigger, greater
7Proto-Indo-Europeanméǵh₂isteros
8Proto-Indo-Europeanméǵh₂sbig, great

via English fickle

StepLanguageWordMeaning
1EnglishfickleQuick to change one’s opinion or allegiance;...
2Middle Englishfikil
3Old Englishficoldeceitful; crafty; false
4Old Englishficianto deceive; bewile, mislead, con
5Proto-Germanicfikōnąto deceive
6Proto-Indo-Europeanpeyǵ-inactive, reluctant
Every word from Proto-Indo-European méǵh₂sEvery word from Proto-Indo-European méǵh₂isterosEvery word from Proto-Italic magisteros