Denethor was named after the Nandorin chieftain of the First Age. The name is Nandorin fit into the Sindarin sound range, and is said to mean "Lithe and lank".
Sindarin
denethor
masculine name. Denethor
Denethor
Denethor
Denethor (Nando)
Denethor (Nando)
In an explanation of the name of Denethor II (who was named after this elf), the Steward of Gondor, it is stated that Denethor is Nandorin fit into the Sindarin sound range, and is said to mean "Lithe and lank". In the earlier The Lost Road, the name Denethor is said to contain the word element Dani. According to The Lhammas, it derives from Primitive Elvish Ndani-thārō, meaning "Saviour of the Dani", as he was the one who led them to the West. Other derivatives of this name are: Daintáro in Telerin, Nanisáro in Qenya, Dainthor in Noldorin and Denipor in Doriathrin.
The 10th and also the 26th (and last) of the ruling stewards of Gondor (LotR/1039), possibly derived from the name of the Nandorin Elf Denethor. Its meaning (if any) as a Sindarin name is unclear; the elements of the Nandorin name do not have any clear Sindarin cognates.
Conceptual Development: The name of the last ruling steward was N. Denethor when he first appeared in Lord of the Rings drafts from the 1940s (TI/375).