Elendil's title Voronda is essentially identical to that of Mardil the first Ruling Steward of Gondor, who was known as Mardil Voronwë, or Mardil the Steadfast. Both titles derive from the same root word, and the slight difference between them is a matter of grammar. Voronda is an adjectival form (so it means precisely 'faithful' or 'steadfast' in English). Voronwë, however, is a noun, so it literally means either 'steadfast one' or 'steadfastness' depending on context (with the former presumably applying in Mardil's case).