casual -
marked by blithe unconcern; "an ability to interest casual students"; "showed a casual disregard for cold weather"; "an utterly insouciant financial policy"; "an elegantly insouciant manner"; "drove his car with nonchalant abandon"; "was polite in a teasing nonchalant manner"
unconcerned lacking in interest or care or feeling; "the average American...is unconcerned that his or her plight is the result of a complex of personal and economic and governmental actions...beyond the normal citizen's comprehension and control"; "blithely unconcerned about his friend's plight"
casual -
not showing effort or strain; "a difficult feat performed with casual mastery"; "careless grace"
easy obtained with little effort or sacrifice, often obtained illegally; "easy money"
casual -
hasty and without attention to detail; not thorough; "a casual (or cursory) inspection failed to reveal the house's structural flaws"; "a passing glance"; "perfunctory courtesy"
unplanned without apparent forethought or prompting or planning; "an unplanned economy"; "accepts an unplanned order"; "an unplanned pregnancy"; "unplanned remarks"
casual -
without or seeming to be without plan or method; offhand; "a casual remark"; "information collected by casual methods and in their spare time"
unplanned without apparent forethought or prompting or planning; "an unplanned economy"; "accepts an unplanned order"; "an unplanned pregnancy"; "unplanned remarks"
casual -
occurring from time to time; "casual employment"; "a casual correspondence with a former teacher"; "an occasional worker"
Casual -
Happening or coming to pass without design.
Casual -
Informal, relaxed.
Casual -
Designed for informal use.
Wikipedia
In the European tradition, casual is the dress code which emphasizes comfort and personal expression over presentation and uniformity. It includes a very wide variety of costume.