Where does “ombra-” come from?

ombra- (Irish) comes from Esperanto -a, from Italian -a, from Latin -a, from Proto-Italic -ā, from Proto-Indo-European -éh₂.

Ancestry of “ombra-”, step by step

Step	Language	Word	Meaning
1	Esperanto	-a	Related to, in the manner of, of; Belonging to,...
2	Italian	-a	Used, with a stem, to form the third-person...
3	Latin	-a	suffixed to the roots of verbs, forms agent...
4	Proto-Italic	-ā	Forms masculine agent nouns from prefixed or compounded bases
5	Proto-Indo-European	-éh₂	—