Where does “unconstantness” come from?

unconstantness (English) comes from English unconstant, from English constant, from Middle English constant, from Old French constant, from Latin cōnstantem.

Ancestry of “unconstantness”, step by step

unconstantness traces back through two separate lines of ancestry.

via English unconstant

StepLanguageWordMeaning
1Englishunconstantinconstant
2EnglishconstantUnchanged through time or space; permanent;...
3Middle Englishconstant
4Old Frenchconstant
5Latincōnstantem

via English Ness

StepLanguageWordMeaning
1EnglishNessAn Ulster princess and the mother of Conchobar mac Nessa and Findchoem in the Ulster Cycle of Irish mythology. Daughter of Eochaid Sálbuide. Also the mother of Cormac Cond Longas by incest with Conchobar mac Nessa
2Middle Englishnesse
3Old Englishnæsnot, not at all; not; first/third-person singular...
4Proto-Germanicnasjąfoothill; headland; cape
5Proto-Indo-Europeannéh₂snose
Every word from Latin cōnstantemEvery word from Old French constantEvery word from Middle English constant