From Latin 'causa' (reason, legal case) — of unknown deeper origin but central to Western philosophy ever since.
A person or thing that gives rise to an action, phenomenon, or condition; a reason for an action or condition; a principle or movement that one supports or advocates.
From Old French 'cause' (cause, reason, motive; lawsuit), from Latin 'causa' (reason, motive, cause; legal case, lawsuit, judicial process). The Latin word's deeper etymology is unknown — it has no accepted PIE root and may be a pre-Latin substrate borrowing. In Roman legal language, 'causa' was the standard term for a legal case or lawsuit, and this juridical sense traveled into English
Italian 'cosa' (thing) descends from Latin 'causa' (cause, legal matter) — the same source as English 'cause.' A legal case became so generic a concept in everyday Italian that it evolved into the word for 'thing' itself, paralleling how 'thing' in English shifted from 'assembly' to 'any object.'