Where does “رضا” come from?

رضا (Ottoman Turkish) comes from Arabic رِضًا, from Arabic رَضِيَ — to be satisfied, to be pleased.

Ancestry of “رضا”, step by step

Step	Language	Word	Meaning
1	Arabic	رِضًا	being pleased; consent, approval
2	Arabic	رَضِيَ	to be satisfied, to be pleased