What does clockwork mean?

[Nasreddin]

Test No. incompl/inter-78 "Tick Tock", question 4

You can always be sure that there'll be a delivery today as the service is as regular as clock..........

(a) time
(b) task
(c) job
(d) work

Test No. incompl/inter-78 "Tick Tock", answer 4

You can always be sure that there'll be a delivery today as the service is as regular as clockwork.

Correct answer: (d) work

Your answer was: incorrect
You can always be sure that there'll be a delivery today as the service is as regular as clockjob.
_________________________

What does it mean?
What the difference betweem clock?

[Torsten]

Clockwork is the machinery that makes a clock run and it has to be very precise and reliable.

The word clockjob does simply not exist.

TOEIC listening, talks: University employee is asking visitor to move vehicle from fire zone

[Kati Svaby]

Hello,

I would like to add two examples and two idioms to clockwork.
clockwork(n)(U)

Exp:
clockwork toys =(toys that you wind up with a key)
working with clockwork = (complete) precision

IDM:=
1.go/run like clockwork = to happen according to plan; to happen without difficulties and problems.
The operation went like clockwork.

2.(as) regular as clockwork = very regularly;happening at the same time in the same way
Exp: He is home by six every day, regular as clockwork.