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.

• from an external source; not innate nor inherent
  
• (biology) developing in an unusual place or from an unusual source
  
• not congenital