i Register
In some senses, ail is marked as obsolete. Watch for register when choosing this word.
verb
To cause to suffer; to trouble, afflict. (Now chiefly in interrogative or indefinite constructions.)
Have some chicken soup. It's good for what ails you.
What aileth thee, Hagar?
To be ill; to suffer; to be troubled.
When he ails ever so little […] he is so peevish.
noun
An ailment; trouble; illness.
adj
Painful; troublesome.