Having no justifying cause or reason:
— A senseless, causeless murder.
— A causeless war that never had an aim.

synonym: reasonless.

Polish: bezprzyczynowy

Having no cause or apparent cause:
— A causeless miracle.

synonyms: fortuitous, uncaused.

Roget 156: casual, fortuitous, accidental, adventitious, causeless, incidental, contingent, uncaused, undetermined, indeterminate; random, statistical; possible etc. 470; unintentional etc. 621.    ... show more

Roget 621: fortuitous etc. 156; unintentional, unintended; accidental; not meant; undesigned, purposed; unpremeditated etc. 612; unforeseen, uncontemplated, never thought of.    random, indiscriminate, promiscuous; undirected; aimless, driftless^†, designless^†, purposeless, causeless; without purpose.    possible etc. 470.    unforeseeable, unpredictable, chancy, risky, speculative, dicey.    ... show more