Our evidence for the establishment of Amon Lhaw as the Hill of Hearing is scant, and consists of a single mention by Aragorn that this happened in the time of the 'great kings' of Gondor (The Fellowship of the Ring II 9, The Great River). Exactly who these Kings might have been is not explained, but the comment likely referred back to the foundational times of Gondor when Isildur and Anárion ruled the kingdom together and constructed many great works. Our best evidence suggests, however, that the nearby Pillars of the Kings were raised by Rómendacil II long after the foundation of Gondor, and it seems at least plausible that this might apply to Amon Lhaw as well. In that case it would have become the Hill of Hearing much later in Gondor's history, in about the year III 1250.

The combination lh represents a palatised l sound. That's a sound that occurs very rarely in English, but it might be approximated by the 'll' sound in the middle of the word 'million'. In Elvish, aw was pronounced approximately to rhyme with the English word 'now'. So the entire word lhaw (literally 'ear') was pronounced something like 'llau'.

The name Amon Lhaw translates literally as the 'Hill of the Ear' (as its counterpart Amon Hen translates as the 'Hill of the Eye'). While Amon Hen is often called the Hill of the Eye, however, the literal meaning 'Hill of the Ear' is not recorded as actually being used, and the name is always given in translation as the 'Hill of Hearing'. Strictly the word lhaw did not refer to a single ear, but (at least according to The Etymologies in volume V of The History of Middle-earth) to a pair of ears.