disease, decease

Disease or disease means illness or sickness--
They didn't find a cure for the disease, but the patient recovered without it.
There is a vaccination for this disease, and the doctor recommends that we get one.

Decease or decease is an old-fashioned word for death--
After the decease of their mother, nothing seemed the same.
They found his will shortly after his decease.

 Now that you know that, you can say--
"The family was convinced that the disease had caused his decease."

Note-- "decrease" means to become or make less or to diminish--
The company offered to keep him on, with a decrease in salary.
Note # 2-- "deceased" means dead--
Are your parents living, or are they deceased?
"Deceased" may also mean a dead person--
Write the name of the deceased here.