Capable of being separated, disconnected, or divided; able to be disjoined.
From disjoin + -able (a suffix meaning 'able to be' or 'capable of being'). The -able suffix creates adjectives indicating possibility or capability.
The -able suffix is endlessly productive—you can add it to almost any verb in English to ask 'is this thing capable of being verb-ed?'—which is why it's so useful for creating new words that everyone immediately understands.
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