If "or" is ignored as the obvious answer here then "Stop" could be the odd one out as it is the only word that can be flipped to get another meaningful word.
Which word does not belong in the following list:
Stop cop mop chop prop shop or crop
Which of the following words does not belong in the list, and why? Reappear Caucasus Inefficiencies Signings Arraigning Horseshoer Intestines Appeases
con top lag rag lap nap