1. having no cause or apparent cause - a causeless miracle - fortuitous encounters--strange accidents of fortune - we cannot regard artistic invention as...uncaused and unrelated to the times • Syn: causeless, uncaused • Similar to: unintended • Derivationally related forms: fortuitousness 2. occurring by happy chance - profits were enhanced by a fortuitous drop in the cost of raw materials • Similar to: fortunate • Derivationally related forms: fortuitousness