Learner's definition of CLOCKWORK
1 : the system of moving wheels inside something (such as a clock or an old-fashioned toy) that makes its parts move 2 — used to describe something that happens or works in a very regular and exact way
— often used before another noun
Every morning, like clockwork, customers line up outside the front door of the bakery.
Their wedding went (off) like clockwork. [=their wedding went very smoothly; everything in the wedding happened the way they planned]
The birds return each year, (as) regular as clockwork.