Source : Webster's Revised Unabridged Dictionary (1913)

Adventitious \Ad`ven*ti"tious\, a. [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.