1. causeless, fortuitous, uncaused, unintended (vs. intended)

usage: 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"

2. fortuitous, fortunate (vs. unfortunate)

usage: occurring by happy chance; "profits were enhanced by a fortuitous drop in the cost of raw materials"

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See also: fortuitous (Dictionary)