adventitious

adj

1. From an external source; not innate or inherent, foreign.
2. Accidental, additional, appearing casually.

   “In a triad of verbs that admits nothing adventitious, Judah sees, takes, and lies with a woman; […]”

   “The discovery of the art of making pottery was probably in all cases adventitious, the clay being first used for some other purpose.”

   “The adventitious disappearance of those nearer the throne than the duke had, moreover, set tongues awagging.”

3. Not congenital; acquired.
4. Developing in an unusual place or from an unusual source.

   “The Velloziaceae have evolved a woody stem which is covered with a layer of adventitious roots mingled with the fibres of the old leaf sheaths;”