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]
" It is never used to express a specific disease. We do not say, a fever ails him; but, something ails him." [1913 Webster]
"What aileth thee, Hagar?" [1913 Webster]

   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." [1913 Webster]

   Indisposition or morbid affection. [1913 Webster]

ail, v.
1 tr. archaic (only in 3rd person interrog. or indefinite constructions) trouble or afflict in mind or body ( what ails him?).
2 intr. (usu. be ailing) be ill.

Etymology:
OE egl(i)an f. egle troublesome

VB  V, be ill, ail, suffer, labor under, be affected with, complain of, have, droop, flag, languish, halt, sicken, peak, pine, gasp, keep one's bed, feign sickness, lay by, lay up, take a disease, catch a disease, catch an infection, break out.

VB  feel pain, suffer pain, experience pain, undergo pain, bear pain, endure pain, smart, ache, suffer, bleed, ail, be the victim of, labor under afflictions, bear the cross, quaff the bitter cup, have a bad time of it, fall on evil days, go hard with, come to grief, fall a sacrifice to, drain the cup of misery to the dregs, sup full of horrors, sit on thorns, be on pins and needles, wince, fret, chafe, worry oneself, be in a taking, fret and fume, take on, take to heart, cark, grieve, mourn, yearn, repine, pine, droop, languish, sink, give way, despair, break one's heart, weigh upon the heart.