Mercury, was the famed messenger of Zeus, the protector of travellers and bringer of luck. He was the son of Zeus and Atlas' daughter Maia, and he was the father of Pan. Maia was traditionally regarded as 'Mother of the Earth', so it is tempting to see Hermes' name as deriving from era, 'earth'.
The widely held origin of his name, however, is not this but herma, 'rock', 'stone'. Hermes was (as a protector of travellers and a messenger) the god of roads, and at certain points on roads a stone heap would be placed to mark a holy spot (something on the lines of a Christian shrine such as the French calvaire).
This stone heap conventionally became a pillar with the representation of a human bust (Hermes), and as well as being a religious or mystical symbol was also a phallic one. However, herma has the basic meaning 'prop', 'support', and the name can thus also be taken metaphorically. But, as so often, the name is very likely not of Greek origin at all.