It is derived from the Old French word "raiment" which, in turn, comes from the Latin "vestimentum," meaning "clothing."
However, "rǣdment" is not commonly used in modern English. It is mostly found in translations of Old English texts or in historical context.
The modern English word "rayment" is still used, but it's considered more archaic and poetic. We generally use words like "clothing," "garments," or "attire" in everyday conversation.