Adventitious

Adventitious is a term that describes an event that occurs by chance, rather than by plan or design. In biology it can refer to parts that are accidentally formed or in an unusual position anatomically. For instance, "Weeds are very adventitious and grow in random and unexpected places." Or let's say in conversation you are suspicious of a person bringing up a subject deliberately when they are making it seem if it came up by chance -- you would question if they subject was adventitious or deliberate.