Allopathic is a snarl word invented by homeopathetic medicine founder Samuel Hahnemann, and used by quacks, to disparage evidence-based medicine, and the real doctors and other trained professionals who practice it.
No one knows what its roots are, but allo is a derivation of the Greek, meaning "different". This was in contrast to the homeo in homeopathic, which means "same", referring to Hahnemann's false theory of "like cures like."
Generally, allopathic medicine refers to "the broad category of medical practice that is sometimes called Western medicine, biomedicine, scientific medicine, or modern medicine"—in other words, it's the stuff that actually works. However, by homeopathy's definition, all non-homeopathic medical ideas must be allopathy, since they aren't based on "like cures like"; this means that, ironically, according to the original definition, every other kind of "alternative" medicine (like herbalism, vitamins, chiropractic, etc.) is also part of allopathy.
The use of the term outside of academic discussion of the philosophy of medicine, or the specific context of osteopathic education as previously mentioned, is generally a dead giveaway that the speaker is a True Believer in alternative medicine.
- Legal Status of Traditional Medicine and Complementary/Alternative Medicine: A Worldwide Review, 2001. Accessed 2007-09-121
- http://jama.jamanetwork.com/article.aspx?articleid=195503 Academic Geriatric Programs in US Allopathic and Osteopathic Medical Schools] citation by way of example