🔼The name Dagon in the Bible
The name Dagon appears in the Bible as belonging to the chief deity of the Philistines. When the Philistines finally caught Samson, they first imprisoned him in Gaza and then paraded him off in the temple of their god Dagon (Judges 16:23). Something similar was done to king Saul, or at least to his head (1 Chronicles 10:10).
Dagon and his temple (in Ashdod, this time) feature predominantly in the story of the abduction of the Ark of the Covenant (1 Samuel 4). Hophni and Phinehas had foolishly taken the Ark as a talisman into battle against the Philistines, but the Philistines prevailed and took the Ark for booty and placed it in the temple of Dagon in Ashdod (1 Samuel 5:2). The next morning, however, they found the statue of Dagon on its face in front of the Ark. They hoisted the statue back in place, but the morning after that they found the statue again on the floor, but this time the head and hands had broken off from the torso.
In the mean time, the Ashdodites came down with all sorts of horrible diseases and they decided to send the Ark first to Gath and then to Ekron, and everybody there too became sick. Finally, after seven months of this, the Philistines sent the Ark back to Israel, where it arrived in Beth-shemesh (1 Samuel 6:9).
🔼Etymology of the name Dagon
Dagon of the Philistines is often assumed to be a kind of fish-god, which was known with some degree of variation from Babylon to Egypt. This fish-god, with the body of a fish but human hands and head, appeared under different names (for instance Odakon), even to the extent that it becomes difficult to establish where one deity ends and the next one begins. Sometimes he is a fertility god, sometimes a storm god and sometimes a maritime god.
There was a fish-god named Dagan in Assyria and Babylon and scholars generally agree that this name came from a root dgn, meaning grain. But in his article on the Philistine Dagon in Hastings Dictionary of the Bible, N. Koenig states that "an identification of this god [Dagon] with the Babylonian Dagan is doubtful". In his book The Cosmology of the Babylonians, Peter Jensen even stated that the Assyrian deity Dagan had nothing to do with a fish-man named Odakon. The Jewish Encyclopedia, on the other hand, declares by no means certain that Dagon, Odakon and the Assyrian Dakan/Dagan were unrelated.
All these sources are somewhat archaic, and HAW Theological Wordbook of the Old Testament helpfully submits that "no modern scholar since the turn of the century [that's 1900] follows Jerome and Kimchi who suggested on the basis of popular etymologizing that he was a fish-god. Many moderns [...] view him as a grain god".
The reason for all this confusion is that the Hebrew rendering of the name of this Philistine deity, דגון, appears to be derived from either the Hebrew word for fish, דג, or grain, דגן, and there's a good chance that these two words are related and both in essence express a multitudinousness:
For a meaning of the name Dagon, NOBSE Study Bible Name List reads Fish and Jones' Dictionary of Old Testament Proper Names proposes a rather elaborate Honored Fish. BDB Theological Dictionary does not offer an interpretation of this name.
In light of the above, however, it seems obvious that the Hebrews (or even the Philistines for that matter) wouldn't understand the name Dagon as "fish" but rather as Abundance. And there's much more to this:
The historical parts of the Bible aren't merely stories that sum up legendary facts, but much rather a commentary on how Yahwism won from the competing religions. By the time the Hebrew Bible was written, Yahwism experienced competition mostly from religions based on celestial deities, and abundance was a proverbial quality of stars (Genesis 15:5). Star-gazing was done by people who lived in darkness (Isaiah 9:2), the people who received the Word of God through parables, whereas the people of Israel received the great light of the Word of God as clearly as light of day (Mark 4:11). This tension between metaphorical stars and sun is clearly expressed in the stories concerning Dagon. This deity was first destroyed by Samson (whose name means Sun), and secondly by the Ark, which returned to Israel via Beth-shemesh (which means House Of The Sun). In that sense, the name Dagon means Astrology, or even more general: Polytheism, which was defeated by the slow but sure progress in theological thought that resulted in the advance of monotheism.
By the time the Biblical Dagon stories received their final form, the Greeks were telling myths about the constellation Pisces (Fish; and the Philistines were most probable of Aegean descent). Their stories told of Aphrodite and Eros who escaped the hundred dragon-headed "father of all monsters" Typhon by jumping into the sea and transforming into the fish that are still visible in the night sky as the constellation Pisces. As noted by Joseph Campbell, the story of the final defeat of Typhon by Zeus finds it Biblical reflections in the story of YHWH defeating Leviathan (Job 41) and Rahab (Isaiah 51:9).
But remember that the victories of YHWH aren't the victories of man. Since revelation occurs gradually, human understanding evolves equally gradually from the darkness of ignorance (hence wars, sickness and poverty) to the light of understanding (hence peace, health and prosperity). The stories of Abraham leaving Ur of the Chaldeans and Israel leaving Egypt tell besides an obvious difference also of a shared origin. Immature understanding must always make way for a mature understanding, but as long as the immatures don't declare war on the matures, the matures will always respectfully remember their ancestry.