Where does “unsufferableness” come from?

unsufferableness (English) comes from English unsufferable, from English suffer, from Middle English suffren, from Old French sofrir, from Vulgar Latin sufferire, from Latin sufferō, from Latin ferō, from Proto-Italic ferō — shiny, light brown.

Ancestry of “unsufferableness”, step by step

unsufferableness traces back through two separate lines of ancestry.

via English unsufferable

StepLanguageWordMeaning
1EnglishunsufferableNot able to be suffered, difficult or impossible...
2EnglishsufferTo undergo hardship; To feel pain; To become...
3Middle Englishsuffrensuffer
4Old Frenchsofrirto suffer
5Vulgar Latinsufferirepresent active infinitive of *sufferiō
6Latinsufferōto put or lay under
7Latinferōto bear; to carry
8Proto-Italicferōcarry, bear
9Proto-Indo-Europeanbʰéretito be carrying
10Proto-Indo-Europeanbʰēr-shiny, light brown

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 Proto-Indo-European bʰēr-