casual

Synonyms: accidental adventitious by chance contingent erratic extemporaneous extempore fluky fortuitous impromptu improvised impulsive incidental infrequent irregular occasional odd offhand serendipitous spontaneous uncertain unexpected unforeseen unintentional unplanned unpremeditated

Antonyms: deliberate painstaking planned premeditated

Synonyms: aloof apathetic blase breezy cool cursory detached down home easygoing folksy homey incurious indifferent informal insouciant lackadaisical laid-back loose low-pressure mellow offhand perfunctory pococurante purposeless remote unconcerned unfussy uninterested withdrawn

Antonyms: formal serious