obtained, done, made, etc., by stealth; secret or unauthorized; clandestine

a surreptitious glance.

acting in a stealthy way.

obtained by subreption; subreptitious.

adjective

aboveboard , authorized , honest , open

adjective

clandestine , covert , fraudulent , furtive , hidden , hole-and-corner , hush-hush * , on the qt , on the sly , private , skulking , slinking , sly , sneaking , stealthy , sub-rosa , unauthorized , undercover , underhand , under-the-table , under wraps * , veiled , secretive , sneaky , concealed , secret