Adventi'tious. adj. [adventitius, Lat.]
That which advenes; accidental; supervenient; extrinsically added, not essentially inherent.
Diseases of continuance get an adventitious strength from custom, besides their material cause from the humours. Bacon.
Though we may call the obvious colours natural, and the others adventitious; yet such changes of colours, from whatsoever cause they proceed, may be properly enough taken in, to illustrate the present subject. Boyle on Colours.
If his blood boil, and th' adventitious fire
Rais'd by high meats, and higher wines, require
To temper and allay the burning heat;
Waters are brought, which by decoction get
New coolness. Dryd. Juvenal, Sat. v.
Of this we have an instance in the gem-kind; where, of all the many sorts reckoned up by lapidaries, there are not above three or four that are original; their diversities, as to lustre, colour, and hardness, arising from the different admixture of other adventitious mineral matter. Woodward's Natural Hist.