The only free and comprehensive online etymological dictionary of the Spanish language
llano (Adjective) "flat"
11th cent. From Latin planus 'id.' From Proto-Italic *plāno- 'id.' From Proto-Indo-European *pleh2-nó- "flattened."
The origin of the surnames de Llano, Llan, Llana, Llanas and Llanos, and of Llanes, a town in Oviedo.
Indo-European
Romance
Asturian llanu, Portuguese chão, Catalan pla, French plan, Italian: piano, Romanian plan
Balto-Slavic
Old Prussian plonis "threshing floor," Lithuanian plónas "thin," Latvian plãns 'id.'