What does adventitious mean?
The definition of adventitious
Ad`ven*ti”tious, a.
Etym: [L. adventitius.]

1 Added extrinsically; not essentially inherent; accidental or causal; additional; supervenient; foreign. To things of great dimensions, if we annex an adventitious idea of terror, they become without comparison greater. Burke.
2 (Nat. Hist.)
Out of the proper or usual place; as, adventitious buds or roots.
3 (Bot.)
Accidentally or sparingly spontaneous in a country or district; not fully naturalized; adventive; — applied to foreign plants.
4 (Med.)
Acquired, as diseases; accidental.

— Ad`ven*ti”tious*ly, adv.
— Ad`ven*ti”tious*ness, n.