Artificial intelligent assistant

check-string

ˈcheck-string
  A string by which the occupant of a carriage may signal to the driver to stop.

1774 Colman Man of Business iii. (D.) The young man was in the high road to destruction..it was time to pull the check-string. 1796 Felton Carriages Gloss., Check String, a worsted line, by which the coachman has notice to stop. 1845 Mrs. Carlyle Lett. I. 358 In passing along Brompton Road, he suddenly pulled the check-string.

Oxford English Dictionary

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