Abarim Publications' online Biblical Greek Dictionary
The noun σεληνη (selene) literally means: "she of flashing [cold] light" and is Greek's common word for moon. It derives from the noun σελας (selas), light, brightness, flame or beacon.
The noteworthy difference between the Greek word for moon and the Hebrew one — namely לבנה (lebanah), which stems from the verb לבן (laban), to be white; hence the name Laban — suggests that the Hebrews understood that the moon is not a light but a reflector of light (namely sunlight), whereas the Greeks appear to have mistaken it for an autonomous beacon of cold fire, which produced a kind of pale and icy light.
Our English words "moon" and "month" and even "menstruate" share their Proto-Indo-European root with the Greek noun μην (men), meaning month.
Our noun σεληνη (selene), meaning moon, is used 9 times in the New Testament, see full concordance, and from it derives:
- The verb σεληνιαζομαι (seleniazomai), which literally means to be moonized, but more commonly is translated as to be moonstruck, i.e. to be bonkers or crazy (Matthew 4:24 and 17:15 only). From the Latin synonym of our parent noun σεληνη (selene), namely luna, comes the equivalent of moonstruck, namely lunatic. The idea behind this word is that the sun represents one's center of reason, around which all other considerations revolve. This center may not always be fully visible (due to clouds, space debris, lack of eyes) but its existence is demonstrated by a stable mind. The mind's "center of gravity", which relates to one's emotional center rather than one's rational one, is determined from the common center of gravity of the sun, moon and other planets. This is the reason why one's feelings and one's convictions are so often misaligned (Romans 7:15-16). This misalignment may be notoriously uncomfortable but it's certainly not a bad thing and actually the very reason why planet earth is alive. But when the heavens clear and one mistakes the moon for one's solar center, the result is not a mere misalignment but a complete dissociation between one's rational and emotional centers. The result is lunacy, which is a condition marked by more and more detail about less and less substance, and more and more feelings for less and less reason.