ailyoudaoicibaDictYouDict[ail 词源字典]
ail: [OE] Now virtually obsolete except in the metaphorical use of its present participial adjective ailing, ail is of long but uncertain history. The Old English verb egl(i)an came from the adjective egle ‘troublesome’, which had related forms in other Germanic languages, such as Middle Low German egelen ‘annoy’ and Gothic agls ‘disgraceful’, aglo ‘oppression’. The derivative ailment did not appear until as late as the 18th century.
[ail etymology, ail origin, 英语词源]
ail (v.)youdaoicibaDictYouDict
c. 1300, from Old English eglan "to trouble, plague, afflict," from Proto-Germanic *azljaz (cognates: 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.
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]