fortuitous
1. [ adjective ] having no cause or apparent cause
Synonyms: uncaused causeless
Examples:

"a causeless miracle" "fortuitous encounters--strange accidents of fortune" "we cannot regard artistic invention as...uncaused and unrelated to the times"

Related terms: unintended
2. [ adjective ] occurring by happy chance
Examples:

"profits were enhanced by a fortuitous drop in the cost of raw materials"

Related terms: fortunate
Similar spelling:   fortuitously
  fortuity
  fortieth
  forthwith