Abarim Publications' online Biblical Greek Dictionary
The adjective σφοδρος (sphodros) means vehement, violent, impetuous or excessive. On rare occasions in the classics this adjective was used in a positive way, in the sense of zealous or robust.
It's not clear where this word comes from, and we here at Abarim Publications liberally surmise that they may very well be of Semitic extraction. Candidates are the Aramaic verb שפד (sapad), to pierce or skewer, and the Hebrew (and Aramaic) verb ספד (sapad), to wail or lament.
The adjective σφοδρος (sphodros), vehement or violent, isn't used in the New Testament, but from it come: