Stealthy means being marked by or acting with quiet, caution, and secrecy intended to avoid notice. See synonyms at http://www.answers.com/topic/secret.
That is the correct spelling of the adjective "stealthy." It means quiet, surreptitious, or difficult to detect.
sneak
A likely word is "stealthy."
As stealthy as a cat
it means you are not as clever or smart as you believe you are
Done by stealth; accomplished clandestinely; unperceived; secret; furtive; sly.
Stealthy is an adjective
Stealthily is the adverb form for stealth. Stealthy is the adjective form. The cat moved stealthily. The cat was stealthy.
You may mean 'infiltration' , which means to enter gradually and imperceptibly by stealthy methods.
The cat had to be stealthy if he was going to catch is prey.
the STEALTHY cat crawled along the hallway
The cat is quite a stealthy and crafty creature! :]