The Collaborative International Dictionary of English v.0.48:

Irk \Irk\ ([~e]rk), v. t. [OE. irken to tire, become tired; cf.
   Sw. yrka to urge, enforce, press, or G. ekel disgust, MHG.
   erklich disgusting; perh. akin to L. urgere to urge, E.
   urge.]
   To weary; to give pain; to annoy.
   [1913 Webster]

         To see this sight, it irks my very soul. --Shak.
   [1913 Webster]

         It irketh him to be here.                --M. Arnold.
   [1913 Webster]

WordNet (r) 3.0 (2006):

irk
    v 1: irritate or vex; "It galls me that we lost the suit" [syn:
         gall, irk]

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "irk":
   abrade, aggravate, ail, annoy, badger, bait, be at,
   be infinitely repetitive, be tedious, be the matter, bedevil,
   beset, bother, bristle, brown off, bug, bullyrag, burn up, chivy,
   complicate matters, concern, devil, discommode, discompose,
   distemper, distress, disturb, dog, drag on, exasperate, exercise,
   fash, fatigue, fret, gall, get, glut, go on forever, gripe, harass,
   harry, heckle, hector, hound, incommode, inconvenience, jade, miff,
   molest, nag, needle, nettle, nudzh, pain, pall, peeve, perplex,
   persecute, perturb, pester, pick on, pique, plague,
   pluck the beard, pother, provoke, put out, put to it, puzzle, ride,
   rile, roil, ruffle, satiate, strain, stress, tease, tire,
   tire to death, torment, trouble, try, try the patience,
   tweak the nose, vex, wear, wear on, weary, worry