Able to happen by chance; possible or liable to occur through luck or fortune rather than design.
From chance (from Old French 'cheance' meaning fall of dice or luck) + -able (Latin suffix -abilis meaning capable or worthy of). The suffix -able has been productive in English since Middle English times.
The word 'chanceable' captures something modern English mostly lost—the medieval sense that the world was full of random chance rather than predictable mechanism; nowadays we'd just say 'possible' and miss that element of luck.
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