A spine-chiller is a story, film, or play made to frighten you — and the frightening is the point, because you are enjoying it. It is the ghost story told late at night, the horror film you watch with a cushion half over your face, the novel you cannot put down even though you now need the hall light on.

The word comes from a picture: real fear feels like something cold running down your back, along your spine. A spine-chiller is a thing that does that to you on purpose.

A few notes on how it is really used. It is a countable noun ('a spine-chiller', 'two spine-chillers'). It has a light, slightly old-fashioned newspaper flavour — the sort of word a film listing or a book review uses, not a word most people say to a friend. In conversation people usually say 'a horror film', 'a scary movie', or 'a thriller'. It also tends to describe the quieter kind of fear: ghosts, suspense, footsteps behind you, rather than blood everywhere. A gory slasher film would more likely be called a horror film than a spine-chiller.

Watch the spelling and the part of speech. The hyphen is usual. And the entry you may have seen describes the adjective — 'a spine-chilling story is very frightening'. The chiller is the thing itself; chilling is what it does.