adjective

1. happening by chance; not planned; incidental a casual visit
2. happening, active, etc. at irregular intervals; occasional a casual worker
3. slight or superficial a casual acquaintance
4. 1. careless or cursory far too casual in his methods
   2. nonchalant; dispassionate affecting casual unconcern
5. 1. informal or relaxed a casual atmosphere
   2. designed for informal occasions or use casual clothes

Etymology: ME & OFr casuel < LL casualis, by chance < L casus, chance, event: see case

noun

1. one who does something only occasionally or temporarily, esp. a casual worker
2. shoes, clothes, etc. designed for informal occasions
3. Mil. a person temporarily attached to a unit, awaiting a permanent assignment or transportation