1 2 and 4 are correct, but only #1 would normally be used.
If one is going to say someone has a ___ , the missing word should be a specific ailment, like "He has a bad cough"
1. He is sick.
2. He has sickness.
3. He has sick.
4. He has a sickness.
5. He has a sick.
(Hello. I have a question. #1 is correct, but what about the others? Which ones are correct?)
2 answers
The forth one is correct and that is it. The other examples are extremely grammatically incorrect.