from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Like a thief; thievish.
- adv. Like a thief; thievishly.
from the GNU version of the Collaborative International Dictionary of English
- Like a thief; thievish; thievishly.
from The Century Dictionary and Cyclopedia
- Like a thief; hence, stealthily; secretly.
thief + -ly (Wiktionary)
If I’m not wrong, you can actually see the thief flourish it in the air before vanishing into the crowd in time-honored thiefly fashion.