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.
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   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]