perfidious

peridious
root: perfidy
pronunciation: 'p&r-f&-dE
function: noun
inflected form(s): plural -dies
etymology: latin perfidia, from perfidus faithless, from per- detrimental to + fides faith -- more at

1 : the quality or state of being faithless or disloyal : TREACHERY
2 : an act or an instance of disloyalty

my sister and i had to look this up tonight while she was translating italian for an aria she is learning (which is just as dorky as it sounds). i thought i'd pass it along for your educational pleasure. i'm pretty sure i used to know what that word meant...