ad·ven·ti·tious 
(ăd′vĕn-tĭshəs, -vən-)
(ăd′vĕn-tĭshəs, -vən-)adj.
1. Arising from an external cause or factor; not inherent: symmetry that was purely adventitious; adventitious circumstances that contributed to the plan's success.
2. Biology
a. Of or belonging to a structure that develops in an unusual place: adventitious roots.
b. Originating from an external source, especially as a contaminant: adventitious viruses in a cell culture.
c. Not congenital: adventitious deafness.
[From Latin adventīcius, foreign, from adventus, arrival; see ADVENT.]
ad′ven·titious·ly adv.
ad′ven·titious·ness n.
adventitiousadventitious roots of a corn plant