WordNet sense 1 (a writer who gives the credit of authorship to someone else):

ghostwriter

WordNet sense 2 (a suggestion of some quality):

touch, trace

WordNet sense 3 (a mental representation of some haunting experience):

shade, specter, spook, wraith, spectre

WordNet sense 4 (haunt like a ghost; pursue):

haunt, obsess

WordNet sense 5 (write for someone else):

ghostwrite