1 always used before a noun : happening by chance : not planned or expected
a casual encounter on the sidewalk
2 (more casual; most casual) : designed for or permitting ordinary dress, behavior, etc. : not formal
a casual restaurant
The atmosphere at the meeting was quite casual.
Note: Casual days are days (such as casual Fridays) when a company allows workers to dress in casual clothes.
3 a (more casual; most casual) : done without much thought, effort, or concern
She takes a casual (=nonchalant) approach to her homework.
He made a casual remark about her shoes.
3 b (more casual; most casual) : not involving a close or serious relationship
They are only casual acquaintances. (=they know each other but not very well)
Their relationship was casual.
3 c (more casual; most casual) : having some interest but not a lot : not serious
He’s a casual sports fan.
4 : happening at certain times but not on a regular basis
She found only casual work.
— casually adjective
I looked casually down at my watch
He was dressed casually in jeans and a sweatshirt.
— casualness noun (noncount)