Where does “dun” come from?

dun (Galician) comes from Galician de, from Old Portuguese de, from Latin dē, from Latin post, from Latin poste, from Proto-Italic posti, from Proto-Indo-European pósti, from Proto-Indo-European pós — afterwards, post; by, at.

Ancestry of “dun”, step by step

Step	Language	Word	Meaning
1	Galician	de	of, from
2	Old Portuguese	de	of
3	Latin	dē	of; concerning; about
4	Latin	post	behind; after, since, besides, except; behind,...
5	Latin	poste	ablative singular of postis
6	Proto-Italic	posti	behind, after
7	Proto-Indo-European	pósti	after
8	Proto-Indo-European	pós	afterwards, post; by, at

Every word from Proto-Indo-European pós →Every word from Proto-Indo-European pósti →Every word from Proto-Italic posti →