Compositional etymology. In the extant manuscript of Orion's Etymologicum, it appears as an elliptic etymology: the real etymon κεραΐζω "to ravage" is substituted by a more frequent synonym βλάπτω "to harm". Thereby, the wording keeps the semantics of the etymology while losing partly the formal aspect, since there is no formal relationship between βλάπτω and κερ-. The full etymology is preserved in the Gudianum (p. 316, see Parallels). The beginning of Orion's explanation, seemingly deriving it from κέρας "horn", is a shortened formulation": κέρας was assumed to be the etymon of κεραΐζω (see κεραΐζω / κέρας), "by metaphor", so that ultimately κέρας is the etymon of the etymon, and this is why it is mentioned here. In the Byzantine Etymologica, under κέρας, the first derivative mentioned is κεραΐζω and the second one is κεραυνός, derivative of κεραΐζω — the ordering of the etymologies is in that case significant. For modern linguistics, κεραυνός indeed belongs with κεραΐζω: both are derived from the same root, although neither is derived directly from the other