Source : Webster's Revised Unabridged Dictionary (1913)

Precarious \Pre*ca"ri*ous\, a. [L. precarius obtained by begging
   or prayer, depending on request or on the will of another,
   fr. precari to pray, beg. See {Pray}.]
   1. Depending on the will or pleasure of another; held by
      courtesy; liable to be changed or lost at the pleasure of
      another; as, precarious privileges. --Addison.

   2. Held by a doubtful tenure; depending on unknown causes or
      events; exposed to constant risk; not to be depended on
      for certainty or stability; uncertain; as, a precarious
      state of health; precarious fortunes. ``Intervals of
      partial and precarious liberty.'' --Macaulay.

   Syn: Uncertain; unsettled; unsteady; doubtful; dubious;
        equivocal.

   Usage: {Precarious}, {Uncertain}. Precarious in stronger than
          uncertain. Derived originally from the Latin precari,
          it first signified ``granted to entreaty,'' and,
          hence, ``wholly dependent on the will of another.''
          Thus it came to express the highest species of
          uncertainty, and is applied to such things as depend
          wholly on future casualties. -- {Pre*ca"ri*ous*ly},
          adv. -- {Pre*ca"ri*ous*ness}, n.

Source : WordNet®

precarious
     adj 1: affording no ease or reassurance; "a precarious truce" [syn:
             {unstable}]
     2: fraught with danger; "dangerous waters"; "a parlous journey
        on stormy seas"; "a perilous voyage across the Atlantic in
        a small boat"; "the precarious life of an undersea diver";
        "dangerous surgery followed by a touch-and-go recovery"
        [syn: {parlous}, {perilous}, {touch-and-go}]
     3: dangerously insecure; "a precarious footing on the ladder"
     4: not secure; beset with difficulties; "a shaky marriage"
        [syn: {shaky}]