Pan

Saying that it comes from the Ancient Greek ποιμήν (poimen - “shepherd”) doesn’t tell the whole story and is possibly inaccurate. Pan is usually thought to have been the Greek descendants of *Péh(2)usōn, a major pastoral god in the Proto-Indo-European pantheon. His name came from the root *peh(2)- (“to shepherd”, “to protect”). While poimen also comes from this root, it did so through the word *poh(2)i-mn. Pan seems to have either come directly from the PIE god’s name or from an unknown variant which also served as the source of Pūsan (Sanskrit for “nourisher”), a Vedic god whose many patronages include the multiplying of cattle.

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Basically, Pan probably doesn’t come from the Ancient Greek word for a shepherd, but from a Proto-Indo-European god whose name might have meant something more akin to “nourisher.” The words are kind of like first cousins.

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(I’m not an etymologist, but this is the impression I have. It may be partially wrong. [noted -ed]

Pan means "bread" in Spanish.

Like Soul said, Pan, with its definition of "all", is used as a prefix.

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Example:
Pandora - all gifted
Pan-all Dorus-gift

It actually means "all" in Greek, as well as "rustic" in Arkadian. That's its real origin.

Could also be a nickname for Pandora, meaning 'all gifts'.

The Greek god Pan was the patron god of shepherds, also associated with music and especially male sexuality. According to Greek mythology, he was a lonely, mischievous god shunned by other deities because of his ugly looks. Despite this, he often tried to pursue beautiful nymphs such as Echo, Pitys, and Syrinx, who all rejected him (though one variation of the myth of Echo and Pan claims that the two had a child together - Iambe, a goddess of verse) but he apparently managed to romance Selene, the goddess of moon, under a disguise which concealed his goat-ish features. He was said to be the son of either Hermes or Zeus and a nymph, and his Roman counterpart was called Faunus. The half-goat Pan later inspired the images of the cloven-hooved Satan in Christian art, though the two had nothing else in common than frightful looks.

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The name of Pan pipes/Pan flute, the musical instrument, is derived from the name of the Greek god, who was associated with the instrument. The word 'panic' is also derived from the god's name, as it was believed that a sudden fear in lonely places was inspired by Pan.

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Pan is also the name of one of Saturn's moons.

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The international English title of Guillermo del Toro's movie 'El Laberinto del Fauno' (Pan's Labyrinth), 2006, bears the name Pan in its title - though none of the actual characters in the movie is called Pan.

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As a prefix, "Pan" means "all", and it usually refers to something involving all the members of a particular group.

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Peter Pan, the title character of James Barrie's novel, is another famous fictional bearer of this name.