The Collaborative International Dictionary of English v.0.48:

Harass \Har"ass\ (h[a^]r"as or h[.a]*r[a^]s"), v. t. [imp. & p.
   p. Harassed (h[a^]r"ast or h[.a]*r[a^]st"); p. pr. & vb. n.
   Harassing.] [F. harasser; cf. OF. harace a basket made of
   cords, harace, harasse,a very heavy and large shield; or
   harer to set (a dog) on.]
   To fatigue; to tire with repeated and exhausting efforts;
   esp., to weary by importunity, teasing, or fretting; to cause
   to endure excessive burdens or anxieties; -- sometimes
   followed by out.
   [1913 Webster]

         [Troops] harassed with a long and wearisome march.
                                                  --Bacon.
   [1913 Webster]

         Nature oppressed and harass'd out with care. --Addison.
   [1913 Webster]

         Vext with lawyers and harass'd with debt. --Tennyson.

   Syn: To weary; jade; tire; perplex; distress; tease; worry;
        disquiet; chafe; gall; annoy; irritate; plague; vex;
        molest; trouble; disturb; torment.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "harassing":
   aggravating, annoying, bothering, bothersome, chafing, disquieting,
   distressful, distressing, disturbing, exasperating, fretting,
   galling, importunate, importune, irking, irksome, irritating,
   pesky, pestering, pestiferous, pestilent, pestilential, plaguesome,
   plaguey, plaguing, provoking, teasing, tiresome, tormenting,
   troublesome, troubling, upsetting, vexatious, vexing, wearisome,
   worrisome, worrying