69 entries under underground topic. ×

11
stealthy(adjective, quiet, clandestine, undisclosed)
9
furtive(adjective, close, clandestine, undisclosed)
7
sneaky(adjective, clandestine, undisclosed)
7
surreptitious(adjective, clandestine, undisclosed)
5
secret(adjective, clandestine, undisclosed, underhand)
5
sly(verb, adjective, move, clandestine, spiriting)
3
clandestine(adjective, undisclosed, skulking)
3
undercover(adjective, clandestine, undisclosed, skulking)
2
covert(clandestine, undisclosed)
2
hidden(clandestine, undisclosed)
2
hush-hush(clandestine, undisclosed, skulking)
2
mystical(clandestine, undisclosed)
2
underhanded(adjective, clandestine, undisclosed)
1
backdoor(close, inside, clandestine, undisclosed)
1
backstairs(close, restricted, inside, clandestine)
1
camouflaged(close, clandestine, undisclosed, furtive)
1
classified(clandestine, undisclosed)
1
close(inside, clandestine, undisclosed, furtive)
1
confidential(restricted, clandestine, discreet, undisclosed)
1
cryptic(close, inside, clandestine, undisclosed)
11 years ago|13k views|share |citing 
APASmart Define. (2015). sneak thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/sneak/thesaurus/synonyms
ChicagoSmart Define. 2015. "sneak thesaurus" https://smartdefine.org/sneak/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2015, sneak thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/sneak/thesaurus/synonyms>.
MLASmart Define. "sneak thesaurus" 10 April 2015. Web. 25 September 2026. <https://smartdefine.org/sneak/thesaurus/synonyms>