casual
adj.
late 14c., "subject to or produced by chance," from Middle French casuel (15c.), from Late Latin casualis "by chance," from Latin casus "chance, occasion, opportunity; accident, event" (see case, n.1).Of persons, in the sense of "not to be depended on, unmethodical," it is attested from 1883; meaning "showing lack of interest" is from 1916. Of clothes, "informal," from 1939. Related: Casually.
〔蒋〕[cas降， -ual形容词后缀;’突然降临的”] 偶然的，未竟然到的
〔李〕[cas=to befall降临；-u-;-al a.=having the quality有……性质的→“having the quality of befalling, or happening by chance带有偶发性质的”→] a.① not planned偶然的