Where does “rarus” come from?

rarus (Latin) comes from Proto-Indo-European h₁reh₁- — to row; to separate; loose, sparse, rare.

Ancestry of “rarus”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	h₁reh₁-	to row; to separate; loose, sparse, rare

rarus — Etymology, Origin & Word History | Etymology Explorer