The Collaborative International Dictionary of English v.0.48:

Vexatious \Vex*a"tious\, a. [See Vexation.]
   1. Causing vexation; agitating; afflictive; annoying; as, a
      vexatious controversy; a vexatious neighbor. "Continual
      vexatious wars." --South.
      [1913 Webster]

   2. Full of vexation, trouble, or disquiet; disturbed.
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            He leads a vexatious life.            --Sir K.
                                                  Digby.
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   Vexatious suit (Law), a suit commenced for the purpose of
      giving trouble, or without cause.
      [1913 Webster] -- Vex*a"tious*ly, adv. --
      Vex*a"tious*ness, n.
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WordNet (r) 3.0 (2006):

vexatiously
    adv 1: in a vexatious manner