Looked on google, saw decubiti, decubitii and decubitus. WHICH is the correct plural form of decubitus? Thanks!

Go back to Google, type in the search terms "decubitus" and "plural." You will find TONS of references mentioning that the only form is decubitus. There is no plural form. The word decubitus is actually an adjective and refers to the position of the patient in bed. Hence "decubitus ulcers" which are found in patients who are frequently or always in bed or in a wheelchair.

Same with my Stedman's dictionary. Decubitus is the only form listed.

Thank you, thank you, thank you!