That comes from outside or from some external source; extrinsically added; extraneous; foreign.

Originally: (of a plant) occurring in a region in which it is not native, but imperfectly naturalized, e.g. restricted to cultivated land, areas around human habitation, etc. In later use also: (of a plant or animal) occurring in but not native to the region in which it appears.

Designating an embryo which develops asexually from a somatic cell of the ovule (e.g. the nucellus) as a result of a form of apomixis which occurs in certain plants.

An adventive plant or animal.