- causeless, fortuitous, uncaused - 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"
Antonym: intended (indirect, via unintended)
- fortuitous - occurring by happy chance; "profits were enhanced by a fortuitous drop in the cost of raw materials"
Antonym: unfortunate (indirect, via fortunate)