A check or restraint that opposes another check, or a verification done to confirm that something has been checked correctly.
From counter- (against) + check. Check comes from Old French eschec, from Persian shah (king), originally a chess term meaning to threaten the king.
Countercheck is the reason doctors use the 'double-check' system in hospitals—one verification prevents catastrophic mistakes, which is why pilots do the same thing before takeoff.
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