Word Origin & History
O.E. eglian "to trouble, plague, afflict," from P.Gmc. *azljaz (cf. O.E. egle "hideous, loathsome, troublesome, painful;" Goth. agls "shameful, disgraceful," agliþa "distress, affliction, hardship," us-agljan "to oppress, afflict"), from PIE *agh-lo-, suffixed form of base *agh- "to be depressed,
be afraid." Related: Ailing (c.1600); ailment formed in Eng. 1706.
"It is remarkable, that this word is never used but with some indefinite term, or the word no thing; as What ails him? ... Thus we never say, a fever ails him." [Johnson]