The American HeritageĀ® Dictionary of the English Language, 4th Edition
n. A bedmate.
n. One that is closely associated or allied with another: "Stupidity here makes an easy bedfellow, as always, with racialismā ( Christopher Hitchens).
n. An associate, often an otherwise improbable one.
the GNU version of the Collaborative International Dictionary of English
n. One who lies with another in the same bed; a person who shares one's couch.
The Century Dictionary and Cyclopedia
n. One who shares a bed with another.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a person with whom you share a bed
n. a temporary associate
Word Usage
"The next morning when the maid came in to make the fire, we woke up face to face in the same bed, and then she told me that her name was Belle Boyd, and I knew for the first time that my bedfellow was the South's famous female spy."