A clock was an instrument for measuring time, sometimes utilising a clockwork mechanism.
Types of clock
The First Doctor kept an ormolu clock in the TARDIS control room. (TV: An Unearthly Child)
The Clockwork Droids used to break clocks to hide their own ticking. (TV: The Girl in the Fireplace)
A spaceship crashed into a London clock tower known as Big Ben. (TV: Aliens of London)
Jack Harkness parked his space craft by Big Ben. (TV: The Empty Child)
Bilis Manger ran a store called A Stitch in Time where he sold clocks. (TV: End of Days)
The Institute for Technological Advancement and Research had a beryllium atomic clock for the countdown to the new millennium. (TV: Doctor Who)
The appearance of a grandfather clock was assumed on at least three occasions by the Master's TARDIS (TV: The Deadly Assassin, The Keeper of Traken, PROSE: The Eight Doctors), although it is unclear as to whether it functioned like a real one when in this form.
General Mariah Learman attempted to build a time machine using clocks and mirrors. (AUDIO: The Time of the Daleks)
Sarah Jane Smith had a scanner watch which could detect aliens. (TV: The Sarah Jane Adventures)
Steven Taylor found the Monk's watch in 1066. (TV: The Time Meddler)
The Doctor's second incarnation had a sundial in his TARDIS. (TV: The Tomb of the Cybermen, The Mind Robber, The War Games)