casual
adj.adj. relaxed and not formal. You use this to describe clothes, behavior, or relationships that are comfortable and not serious.
adj. relaxed and unconcerned in manner; not formal or premeditated. Often used to describe attire, interpersonal dynamics, or employment that lacks a permanent or serious commitment.
The office has a casual dress code on Fridays.
They decided to keep their relationship casual instead of making any long-term plans together.
His casual remark about the project's failure suggested a surprising lack of concern for the months of effort the team had invested.
From Middle French casuel, from Late Latin cāsuālis (“happening by chance”), from Latin cāsus (“event”) (English case), from cadere (“to fall”) (whence English cadence).
Typically precedes the noun it modifies; when describing employment, it implies a lack of fixed hours or benefits.