Where does “Arran” come from?

Arran is of uncertain origin, possibly from Middle Persian ʾldʾn, though the semantic connection and etymological path remain unclear.

Ancestry of “Arran”, step by step

Step	Language	Word	Meaning
1	Middle English	arayne	—
2	Old French	araigne	—
3	Latin	arānea	—
4	Ancient Greek	ἀράχνη	spider; a spider's web