Where does “unuseable” come from?

unuseable (English) comes from English un — One.

Ancestry of “unuseable”, step by step

unuseable traces back through two separate lines of ancestry.

via English un

StepLanguageWordMeaning
1EnglishunOne

via English useable

StepLanguageWordMeaning
1EnglishuseableAlternative spelling of usable
Every word from English un