Third person singular present tense: takes apart something that is assembled or puts it into separate components.
From dis- + assemble + -s. Assemble comes from Old French assembler, so disassemble means to reverse that process.
IKEA furniture probably made 'disassemble' a verb most people know—before flat-pack furniture, we mostly just left things assembled, but now millions of people disassemble and reassemble things regularly.
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