Here are some examples:
* illogical: not logical
* illiterate: unable to read or write
* ill-tempered: having a bad temper
* ill-fated: destined for misfortune
* illness: a state of being sick
It's important to note that "ill-" is not always used in a negative sense. Sometimes it can simply indicate lack of or not having. For example:
* ill-defined: not clearly defined
* ill-equipped: not having the necessary equipment
The exact meaning of "ill-" depends on the specific word it is attached to.