The Collaborative International Dictionary of English v.0.48:

Parlous \Par"lous\, a. [For perlous, a contr. fr. perilous.]
   [1913 Webster]
   1. Attended with peril; dangerous; as, a parlous cough.
      [Archaic] "A parlous snuffing." --Beau. & Fl.
      [1913 Webster]

   2. Venturesome; bold; mischievous; keen. [Obs.] "A parlous
      boy." --Shak. "A parlous wit." --Dryden. -- Par"lous*ly,
      adv. [Obs.] -- Par"lous*ness, n. [Obs.]
      [1913 Webster]