(1):

(a.) Acquired, as diseases; accidental.

(2):

(a.) Out of the proper or usual place; as, adventitious buds or roots.

(3):

(a.) Accidentally or sparingly spontaneous in a country or district; not fully naturalized; adventive; - applied to foreign plants.

(4):

(a.) Added extrinsically; not essentially inherent; accidental or causal; additional; supervenient; foreign.