Alethia

From Srafopedia

When Lyra first shows her Alethiometer to gyptians Farder Coram and John Faa, Faa wants to know the meaning of its name. Coram says he expects it combines the Greek word for truth, "aletheia", with "meter", making it a “truth-measure” (NL 126/GC 125).

Sir Charles Latrom also didn't know what the Alethiometer he stole from Lyra was called, or preteneds not to, because when he is making his demand for the subtle knife in exchange for its return, he asked Lyra its name, and then made the same connections as did Coram between its name and function (SK).