OSIS or variant may refer to:
The suffix ' is used for forming a number of medical terms. The suffix itself signifies only a general functional disorder, but the constructed words are more specific. It is often used to denote a biological process (i.e. Apoptosis, Phagocytosis, Necrosis...)
Osis (feminine: Ose) is a Latvian language surname meaning "ash" (tree; Fraxinus excelsior).