Abarim Publications' online Biblical Greek Dictionary
The curious noun ασελγεια (aselgeia) describes wantonness or licentiousness: a being morally unrestrained, and thus prone to acts of violence and particularly sexual violence. This unpleasant word comes from the adjective ασελγης (aselges), wanton, brutal, outrageous, and obviously relates to the verb ασελγω (aselgo), to assault (sexually). Neither the adjective nor the verb is used in the New Testament. The noun ασελγεια (aselgeia) occurs 10 times; see full concordance.
It's unclear where these words come from or how they were formed (there are no words in Greek that start with σελγ-, selg- or σηλγ-, selg-), but perhaps their formation was helped by the similarity to the adjective ασεληνος (aselenos), meaning moonless (descriptive of a dark night and hence unchecked threats), from σεληνη (selene), moon, in turn from σελας (selas), beacon light.