Where does “رِطْل” come from?

رِطْل (Arabic) comes from Aramaic רִיטְלָא, from Ancient Greek λίτρα, from Proto-Italic *līðrā.

Ancestry of “رِطْل”, step by step

Step	Language	Word	Meaning
1	Aramaic	רִיטְלָא	—
2	Ancient Greek	λίτρα	litra, a Sicilian silver coin; libra, a unit of...
3	Proto-Italic	*līðrā	—