ail (v.)

c. 1300, from Old English eglan "to trouble, plague, afflict," from Proto-Germanic *azljaz (source also of Old English egle "hideous, loathsome, troublesome, painful;" Gothic agls "shameful, disgraceful," agliþa "distress, affliction, hardship," us-agljan "to oppress, afflict"), from PIE *agh-lo-, suffixed form of root *agh- (1) "to be depressed, be afraid." Related: Ailed; ailing; ails. From late Old English also of mental states and moods.

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]

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Definitions of ail from WordNet
ail (v.)
be ill or unwell;
ail (v.)
cause bodily suffering to and make sick or indisposed;
Synonyms: trouble / pain
ail (n.)
aromatic bulb used as seasoning;
Synonyms: garlic