RichThesaurus
cloak-and-dagger
vs
off-the-books
cloak-and-dagger
adj
Marked by menacing furtive secrecy, often with a melodramatic tint or espionage involved.
off-the-books
How often have the words
cloak-and-dagger
and
off-the-books
occurred in a corpus of books?
(source:
Google Ngram Viewer
)