The most sick. The sickest. In the reverse manner, sick being desired, to be more sick is better.

Conjugation of Ill
Ill, Iller Illest
I thought I was Ill with that gear but dat dawg is the illest cat around.
by Jungle Jimm July 18, 2003
Get the illess mug.
The best girl in the world who of which never gave up until now
by Jf33 March 13, 2017
Get the illesse mug.