14th cent. Old Spanish ralo; very late 15th cent. raro. The intervocalic dental was uncertain, curiously leading to two native reflexes of the same Latin word. Raro and ralo were free variants until Modern Spanish and never distinctly separate. From Latin rarus "scattered," "rare," "thin."
Of unknown origin.
Romance: Western Vulgar Latin: Asturian ralu, raru, Portuguese ralo, raro, Galician raro, Catalan rar, French rare, Italian raro ; Eastern Vulgar Latin: Aromanian rar, Romanian rar ; Sardinian: raru