Adventitious, adj. meaning “happening by chance”, “associated by chance”, “coming from another source”; or, in biology, “appearing sporadically or in an abnormal or unusual place”; from the Latin adventicius, meaning foreign. [see, et, et]
To an intellectual person the whole business of love-making is ridiculous, and without dignity. Dreams and fancies are invoked to give it an adventitious interest, and so a sort of mesmerism is exercised, and blissful dreams of eternal happiness come into existence, depending for their duration very much upon the sympathy between the imaginations of the lovers, which sometimes is powerful enough to build up a reality from a vision. However this may be, when love comes in at the door intellect flies out of the window or sleeps the sleep of the disgusted. When it returns to its habitation it delivers stern judgment on the follies that have been committed in its absence.
— Florence Farr, The Dancing Faun [via]