[sodii]

-itis refers to a specific physiological phenomenon: Inflammation (https://en.wikipedia.org/wiki/Inflammation)

swelling can happen without inflammaion, and mild inflammation may occur without noticable swelling.

-osis is a generic suffix for a process or condition: metamorphosis, scoliosis, hypnosis.

[rubberpoliceman]

> and mild inflammation may occur without noticable swelling.

Calor, dolor, rubor, tumor

[sodii]

They are not definition. Maybe they were, when we didn't know about cytokines and immune cells.