I had always thought this word carried the connotation of surprise, but the definitions seem to belie that.
adventitious, a.
1. Of the nature of an addition from without; extrinsically added, not essentially inherent; supervenient, accidental, casual. Cf. the obs. ADVENTIVE.
2. Law. (See quot. 1751.) 1751 CHAMBERS Cycl., Adventitious, in the Civil Law, is applied to such goods as fall to a man, either by mere fortune, or by the liberality of a stranger, or by collateral, not direct succession. In this sense the word stands opposed to Profectitious; by which are signified such goods as descend in a direct line.
3. Nat. Hist. Appearing casually, or out of the normal or usual place, esp. in Bot. of roots, shoots, buds, etc. produced in unusual parts of the plant.
Neh 