The Collaborative International Dictionary of English v.0.48:

Ail \Ail\, n.
   Indisposition or morbid affection.             --Pope.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ail \Ail\ ([=a]l), v. t. [imp. & p. p. Ailed ([=a]ld); p. pr.
   & vb. n. Ailing.] [OE. eilen, ailen, AS. eglan to trouble,
   pain; akin to Goth. us-agljan to distress, agls troublesome,
   irksome, aglo, aglitha, pain, and prob. to E. awe. [root]3.]
   To affect with pain or uneasiness, either physical or mental;
   to trouble; to be the matter with; -- used to express some
   uneasiness or affection, whose cause is unknown; as, what
   ails the man? I know not what ails him.
   [1913 Webster]

         What aileth thee, Hagar?                 --Gen. xxi.
                                                  17.
   [1913 Webster]

   Note: It is never used to express a specific disease. We do
         not say, a fever ails him; but, something ails him.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ail \Ail\, v. i.
   To be affected with pain or uneasiness of any sort; to be ill
   or indisposed or in trouble.
   [1913 Webster]

         When he ails ever so little . . . he is so peevish.
                                                  --Richardson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ail
    n 1: aromatic bulb used as seasoning [syn: garlic, ail]
    v 1: be ill or unwell
    2: cause bodily suffering to and make sick or indisposed [syn:
       trouble, ail, pain]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "ail":
   ache, afflict, agonize, anguish, be affected with, be the matter,
   beset, bite, blanch, blench, bother, burn, chafe, complain of,
   complicate matters, concern, convulse, crucify, cut, discommode,
   distress, disturb, excruciate, feel ill, feel pain, feel the pangs,
   fester, fret, gall, give pain, gnaw, grate, grimace, grind, gripe,
   harass, harrow, have a misery, hurt, inconvenience, inflame,
   inflict pain, irk, irritate, kill by inches, labor under, lacerate,
   martyr, martyrize, nip, pain, perplex, perturb, pierce, pinch,
   plague, pother, pound, prick, prolong the agony, put out,
   put to it, put to torture, puzzle, rack, rankle, rasp, rub, shoot,
   shrink, smart, stab, sting, suffer, thrill, throb, tingle, torment,
   torture, trouble, try, tweak, twinge, twist, twitch, upset, vex,
   wince, worry, wound, wring, writhe