plomo.

From Latin plumbum. The initial group ⟨pl-⟩ usually became ⟨ll-⟩ in inherited Spanish, so a fully popular development would give *llomo or similar. The form plomo points to a semi-learned term taken early from Latin, or to a borrowing through medieval Catalan (see plom) or Aragonese. A Mozarabic origin is unlikely, since the expected Mozarabic form would be *plombo, although the region is relevant because most of the lead in Spain came from Almería in Andalusia. A conservative pronunciation might have persisted among educated speakers, which would also explain the retention of ⟨pl-⟩ as, compare also plaza; there is also retention of ⟨cl-⟩ in words such as claro.