The basic meanings of factitious are "artificial," "contrived," "not spontaneous": "The centerpiece on the table was made of factitious leaves and flowers." "Many gadgets in the home are but factitious conveniences." Fictitious has a related meaning of "not real," but it is more often applied to works of the imagination, such as novels, plays, and stories: "His account of the experience was partly accurate and partly fictitious." A factitious lawsuit is one that has been contrived with little basis in fact; a fictitious lawsuit is one that has à completely imaginary basis.
Dictionary of problem words and expressions. Harry Shaw. 1975.