Source : Webster's Revised Unabridged Dictionary (1913)

Unprincipled \Un*prin"ci*pled\, a. [Pref. un- not + principled.]
   Being without principles; especially, being without right
   moral principles; also, characterized by absence of
   principle. -- {Un*prin"ci*pled*ness}, n.

Source : WordNet®

unprincipled
     adj 1: lacking principles or moral scruples; "freedom from coarse
            unprincipled calumny"- A.E.Stevenson [ant: {principled}]
     2: having little or no integrity