I was interested in the following sentence which appeared in a news article titled “SCIENCE WATCH; PROGRESS IN AIDS DISPUTE” in The New York Times (March 10, 1987).
Dr. Robert Gallo at the cancer institute later isolated the same virus and asserts that his laboratory first demonstrated unequivocably the role of the virus in causing AIDS.
After searching on Oxford Dictionaries, I have found no item for "unequivocably", but I got a lot of hits (139.000) from Google; so I am wondering if "unequivocably" is in common usage nowadays.
Can someone clarify this question? Or is "unequivocably" a common error?