adjective.
Marked by or acting with quiet, caution, and secrecy intended to avoid notice. synonym: secret.
The Century Dictionary and Cyclopedia
Acting by stealth; sly; secretive in act or manner; employing concealed methods: as, a stealthy foe; characterized by concealment; furtive: as, a stealthy proceeding; a stealthy movement.
the GNU version of the Collaborative International Dictionary of English
adjective.
Done by stealth; accomplished clandestinely; unperceived; secret; furtive; sly.