A clock is a stationary device used to keep track of the passage of time. It was commonly used on the planet Earth. The mobile version of a clock is called a wristwatch or simply watch.
In 2121 Henry Archer kept a clock on a wall in his home on Earth. (ENT: "Broken Bow")
By 2151 clocks were use on the Akaali homeworld. (ENT: "Civilization")
In 2254 a female crewmember aboard the USS Enterprise was wearing a wristwatch while off duty. (TOS: "The Cage")
By the 23rd century, clocks were used aboard starships in the form of on-board chronometers. (TOS: "Balance of Terror")
In the remastered version of "The Naked Time", Sulu's chronometer featured a stardate clock and military time.
In 2267, Korob wore a wristwatch. (TOS: "Catspaw")
James T. Kirk kept an antique clock in his home during his first retirement from Starfleet. Sometime prior to 2293, he gave the clock to his friend, Leonard McCoy. (Star Trek Generations)
In 2364, Beverly Crusher wore a wristwatch. (TNG: "Code of Honor")
Marla Aster kept an old clock with a large base in her house on Earth. (TNG: "The Bonding")
Doctor Noonian Soong kept a cuckoo clock in his laboratory on Terlina III. (TNG: "Brothers")
While under the influence of the Saltah'na energy sphere, Benjamin Sisko built a complex mechanical clock, the Saltah'na clock, which he would keep in his office in perpetuity. When asked later why he had done so, he replied "I have no idea." (DS9: "Dramatis Personae")
In an alternate timeline Jake Sisko owned two clocks in his house in Louisiana. One was placed on the wall next to the door and a larger one with a base in his living room. (DS9: "The Visitor")
When Kathryn Janeway and Tuvok were taken to the Q Continuum, a building they were led to had a clock without hands. (VOY: "Death Wish")
In an alternate timeline, Captain Kathryn Janeway was moved by her first officer Chakotay's defiance when she found the watch that he replicated against her direct order to salvage it. (VOY: "Year of Hell, Part II")
Some story titles that are allusions to clocks include: