treachersome

From treacher +‎ -some.

treachersome (comparative more treachersome, superlative most treachersome)

1. Characterised or marked by treachery; treacherous
   • 1910, Mary Esther Miller MacGregor, Lizbeth of the Dale:

     Tom was now holding forth hotly upon the "onparalleled [sic] rascality and treachersome villainousness" of the Opposition in the Ontario Legislature. Elizabeth, her eyes alight, ran swiftly past the gate towards her father.

   • 1919, Ruth Belmore Endicott, Carolyn of the Sunny Heart:

     I do wish you'd come away, Princey ! ” said the little girl anxiously. “I b'lieve he's one of those treachersome dogs that you never know what they mean ― There!

   • 1992, Elizabeth Madox Roberts, M. E. Bradford, The Great Meadow:

     Ko-kosh was treachersome but I could outwit his kind. I kept a close watch. He stole back my knife but I got it again. I wanted a gun. I couldn't come south without I had a gun and I couldn't hunt my food. We went north on the Lake of the Hurons.

   • 2012, Lou Cameron, Stringer and the Wild Bunch:

     Kid Curry dismounted. “Stay put whilst I shed some light on the subject. The clay footing around here is sort of treachersome when it's this wet. [...]”