Abarim Publications' online Biblical Greek Dictionary
The noun ρομφαια (romphaia) describes a kind of sword, or rather something in between a spear and a sword (and a scythe): a kind of weapon that consisted of a sword-like blade attached to a spear-like stick: good for both thrusting and slashing. A more common word for sword in the New Testament is μαχαιρα (machaira), although that word rather denotes a utility knife or pair of scissors.
The Rhomphaia is mentioned 7 times in the New Testament, see full concordance, significantly as the sword that would pierce Mary's soul, "so that the thoughts of many hearts may be revealed" (Luke 2:35), and as the sword that is wielded by angels and coming out of the mouth the White Horseman in the Book of Revelation.
The significance of this is that the Rhomphaia was a very specific weapon and used almost exclusively by the Thracians, who were a broadly diverse collection of tribes (up to 200 of them), which shared a culture and probably spoke mutually legible languages, and were in that regard not unlike the Celts, or even the Hebrews (i.e. sons of Eber). Their language was Indo-European and their heartland was the Balkans. Their word ρομφαια (romphaia) probably resulted in the Latin verb rumpo, to break, burst, tear, rupture, which was highly favored among the poets of the early Roman Empire, who used it all the time.
Since the Bible concentrates wholly on the evolution of information technology, and thus the formation of the alphabet — see our articles on the names YHWH, Logos, Hellas, Philistine, or the verbs αιρεω (haireo), γινωσκω (ginosko), or γραφω (grapho) — the Rhomphaia serves in the New Testament rather obviously as metaphor of the Thracian language.
Which crucial contribution to modern information technology the Thracian language has made is no longer clear — but to give a hint as to the general nature of such a contribution, here at Abarim Publications we suspect that the Shunammites may have been remembered for their work on the development of the glyph, whereas the Gittites may have been immortalized for pioneering vowel notation.
Obviously paralleled by the White Horseman (Revelation 19:11-21), the Thracian Horseman is a frequently deployed artistic expression in reliefs and stelae, and was notably popular in Philippi (whose name means Lovers Of Horses). The Thracian Horseman was commonly depicted as thrusting a Rhomphaia toward a serpent between the legs of the horse — see our article on the noun δρακων (drakon), dragon or serpent — and this striking image morphed in the Christian era into the iconography of Saint George.
In late antiquity, the Thracians enjoyed their own kingdom, namely the Odrysian kingdom (480 - 340 BC), until it too fell to Macedon. This kingdom's emblem was the labrys, a double-headed axe, which is significant to our story because the Rhomphaia was never double-edged, and the paradoxical "double-edged Rhomphaia" mentioned in Revelation 1:16, 2:12 and 19:15 may very well have referred to the signature labrys of the Odrysian kingdom.
In Hellenistic Thrace, the double-headed axe was a signature attribute of the principal deity Zalmoxis, who, like Hadad, Zeus and thus Jupiter and ultimately also YHWH (Psalm 29:3), was the god of thunder (also see our article on νεφελη, nephele, cloud). More significantly, however, was that the Thracians appear to have had no other gods and were thus essentially monotheistic.
The double-headed axe (basically a bow tie on a stick; not an unlikely candidate for the origin of the familiar emblem of the double headed eagle) may have reminded of a stylized representation of how multiple and widely dispersed and different peoples (the curved outer edges of the axe heads) may find a common center in some central governing authority: the knob of the bow tie plus the staff (the similar Latin fasces represents the yet very different idea of forcibly binding the subsidiary tribes tightly around the central staff).
That this central Odrysian authority was not one of brutal tyranny but rather on wisdom, and specifically wisdom that had to be patiently eased out of the observations of society at large (precisely identical to how modern scientists establish natural law) is demonstrated by our word labrys, which (most probably) gave rise to the word labyrinth. The story of Theseus killing the Minotaur at the heart of the Cretan labyrinth is obviously the same story as the Thracian Horseman killing the dragon, and of course YHWH killing Rahab (Isaiah 51:9: "was it not thou who cut Rahab in pieces, who pierced the dragon?").