Capable of decaying; subject to decomposition or deterioration.
From decay + -able (capable of being). Decay comes from Old French decair, from Latin de- + cadere (to fall). The -able suffix makes it an adjective meaning 'capable of'.
All organic material is technically decayable, but some things decay so slowly (like plastic) that 'decayable' almost doesn't apply to them—which is why we have such a trash problem.
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