E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Harpocrates (4 syl.).
The Greek form of the Egyptian god Har-pi-kruti (Horus the Child), made by the Greeks and Romans the god of silence. This arose from a pure misapprehension. It is an Egyptian god, and was represented with its finger on its mouth, to indicate youth, but the Greeks thought it was a symbol of silence.
I assured my mistress she might make herself perfectly easy on that score [his mentioning a certain matter to anyone], for I was the Harpocrates of trusty valets.Gil Blas, iv. 2 (1715).