A lewd insulting gesture made by holding up the middle finger with the others folded down, and meaning ''fuck you'' or ''up yours''; the FINGER Then he put his arm out the window and raised his hand in the one-finger salute (1980s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Examples from the web for one-finger salute
He said Bush gave him the one-finger salute, and they killed the bill.