What does ail mean?
The definition of ail
Ail, v. t.
[imp. & p. p. Ailed; p. pr. & vb. n. Ailing.] Etym: [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.

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. What aileth thee, Hagar Gen. xxi. 17.

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

Ail, v. i.
To be affected with pain or uneasiness of any sort; to be ill or indisposed or in trouble. When he ails ever so little . . . he is so peevish. Richardson.
Ail, n.
Indisposition or morbid affection. Pope.