thiefly

From Middle English thefly; equivalent to thief +‎ -ly.

thiefly (comparative more thiefly, superlative most thiefly)

1. (now rare) Like a thief; thievish.
   • 1893, “The Lay of a Lake Forest Burgler”, in Town Topics, the Journal of Society, volume 30, page 24:

     Most patiently, with noiseless tread, I then did Make thro' those sumptuous halls my thiefly way, Until at last I reached the chamber splendid Where Hobart Chatfield Chatfield slumb'ring lay.

   • 1949, Young Men's Mutual Improvement Association, The Improvement Era - Volume 52, page 378:

     In bantering gusto he went right on with his thiefly enterprise.

   • 1995, Coleman Charlton, ‎Pete Fenlon, ‎S. Marvin, Rolemaster Standard Rules, →ISBN:

     Rogues are characters with some expertise in thiefly abilities and more specialized knowledge of arms than that possessed by Fighters.

   • 2002, Milton Finch, ‎Virginia Ward, Hello Again, Already!: A Book for the Spiritually-Minded Christian

     It would be a sad thing to enter this dark time and then to have an eternal reality stolen and lessened in a thiefly sort of way at the door of death through a life that was lived in a less than honorable fashion.

   • 2011, Ed Greenwood, Elminster: Making of a Mage, →ISBN:

     ...here he was, bent on one last thiefly act.

thiefly (comparative more thiefly, superlative most thiefly)

1. (obsolete) Like a thief; thievishly.
   • 2008, Derek G. Neal, The Masculine Self in Late Medieval England, page 43:

     Downyng described Sybbesoun as "a strong thief to Wood Mill, for truly he and his wife have procured my servant and my goods, that is to say wheat and rye by the bushel and the half, as thiefly and as un-truly as he might do."

• heftily