The Collaborative International Dictionary of English v.0.48:

Besetting \Be*set"ting\, a.
   Habitually attacking, harassing, or pressing upon or about;
   as, a besetting sin.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Beset \Be*set"\, v. t. [imp. & p. p. Beset; p. pr. & vb. n.
   Besetting.] [AS. besettan (akin to OHG. bisazjan, G.
   besetzen, D. bezetten); pref. be- + settan to set. See
   Set.]
   1. To set or stud (anything) with ornaments or prominent
      objects.
      [1913 Webster]

            A robe of azure beset with drops of gold.
                                                  --Spectator.
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            The garden is so beset with all manner of sweet
            shrubs that it perfumes the air.      --Evelyn.
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   2. To hem in; to waylay; to surround; to besiege; to
      blockade. "Beset with foes." --Milton.
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            Let thy troops beset our gates.       --Addison.
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   3. To set upon on all sides; to perplex; to harass; -- said
      of dangers, obstacles, etc. "Adam, sore beset, replied."
      --Milton. "Beset with ills." --Addison. "Incommodities
      which beset old age." --Burke.
      [1913 Webster]

   4. To occupy; to employ; to use up. [Obs.] --Chaucer.
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   Syn: To surround; inclose; environ; hem in; besiege;
        encircle; encompass; embarrass; urge; press.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "besetting":
   annoying, average, backbreaking, common, crushing, current,
   dominant, epidemic, grueling, heavy, hefty, irksome, normal,
   onerous, oppressive, ordinary, painful, pandemic, plaguey, popular,
   predominant, predominating, prevailing, prevalent, rampant,
   regnant, reigning, rife, routine, ruling, running, standard,
   stereotyped, troublesome, trying, usual, vexatious