"Against decay" is probably the best I can do from the Latin route of the word.
In medical terms it's a medicine that is applied to the skin or they wound that has antimicrobial properties. Idodine and Hydrogen Peroxide are good examples.
This is distinguised from Disinfectants, which are by definition used on surfaces and instruments, but not on people -- and from antibiotics which may be administed internally and act systemically.