lay a ghost

lay the ghost of (something) to rest

To do something that finally eliminates one's long-held fears, worries, or distress about something that happened in the past. New DNA evidence in the decades-old investigation finally laid the ghost of these accusations to rest for Mr. Jones. It wasn't until I got my new job that I could finally lay the ghost of my departure from the bureau to rest.
See also: ghost, lay, of, rest

lay a (or the) ghost

get rid of a distressing, frightening, or worrying memory or thought.
The image here is of exorcizing an unquiet or evil spirit.
See also: ghost, lay