Adjective : a furtive, thievish look.    From Dictionary.com. 

You, Who have granted us artists but a single faculty — that of aping You, of playing the Creator-and Who then freakishly and thievishly rob us of the power to do it.    From Wordnik.com.  [Succedaneum] Reference

No. Instead of promoting widespread benefits, they are, for the most part, striving to become billionaires (called "kleptocrats" in a related Wikipedia citation below as they are thievishly parasitic on the body politic).    From Wordnik.com.  [On Rejecting "The System"] Reference

They are thievishly inclined as we have experienced.    From Wordnik.com.  [The Journals of Lewis and Clark, 1804-1806] Reference

For few hounds, so closed, waste and destroy more grapes than many foxes should destroy that come and eat thereof thievishly.    From Wordnik.com.  [Mediaeval Lore from Bartholomew Anglicus] Reference

Prior to the days of Bluetooth, men and women thievishly exchanged contact information on a piece of paper or just whispered their phone number to each other.    From Wordnik.com.  [Thomas P.M. Barnett :: Weblog] Reference

Dutch gave them beads, knives, and other trifles; but they found them thievishly disposed, much like the natives of the Ladrones, and were so fond of iron, that they stole the nails from the cabin windows, and the bolts from the doors.    From Wordnik.com.  [A General History and Collection of Voyages and Travels — Volume 10 Arranged in systematic order: Forming a complete history of the origin and progress of navigation, discovery, and commerce, by sea and land, from the earliest ages to the present time.] Reference

Is it, perhaps, because you attacked me on the open plain, in order to rob me of my invisible bird's nest? or is it because you thievishly endeavored to seduce away the shadow with which I had entrusted you -- my own property -- confiding implicitly in your honor?.    From Wordnik.com.  [Stories by Foreign Authors: German — Volume 2] Reference

Is it, perhaps, because you attacked me on the open plain, in order to rob me of my invisible bird's nest? or is it because you thievishly endeavoured to seduce away the shadow with which I had entrusted you -- my own property -- confiding implicitly in your honour!.    From Wordnik.com.  [Peter Schlemihl] Reference

It showed luxury running riot amongst a nobility already impoverished and ever more thievishly inclined, a colossal capitalism clutching at the land and stretching out its tentacles for every source of profitable trade, the middle class fleeing from the country districts and ousted from their living in the towns, and the fair island that was almost a part of their Italian home, its garden and its granary, in the throes of a great slave war.    From Wordnik.com.  [A History of Rome During the Later Republic and Early Principate] Reference

But thievishly loiter and lurke.    From Wordnik.com.  [A Short History of English Agriculture] Reference

The scattered grain, and thievishly resolved.    From Wordnik.com.  [The Aldine, Vol. 5, No. 1., January, 1872 A Typographic Art Journal] Reference