1. a strongbox.
  2. a rented post-office box equipped with a lock.
  3. Also called lockout box. Television. a closed box, usually fitted with a lock, containing electronic equipment to unscramble cable television pictures for subscribers only: used especially to prevent children from watching programs with explicit sexual content.

Origin of lockbox

An Americanism dating back to 1870–75; lock1 + box1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018