Where does “отбо́р” come from?

отбо́р (Russian) comes from Russian отбира́ть, from Russian от-, from Proto-Slavic otъ-.

Ancestry of “отбо́р”, step by step

Step	Language	Word	Meaning
1	Russian	отбира́ть	—
2	Russian	от-	away from
3	Proto-Slavic	otъ-	—