RichThesaurus
surreptitiously
vs
unofficially
surreptitiously
adv
In a surreptitious manner; stealthily, furtively, secretly.
unofficially
adv
In a way that is not official.
How often have the words
surreptitiously
and
unofficially
occurred in a corpus of books?
(source:
Google Ngram Viewer
)