The story
PIE word *h₁én From in- (prefix meaning ‘in, into; towards’) + flood (“overflow of water from a lake or other body of water; flowing in of the tide; to overflow; to cover or partly fill as if by a flood”). Compare Saterland Frisian Íenfloud (“influence”), West Frisian ynfloed (“influence”), Dutch invloed (“influence”), Middle Low German invlôt (“influence”), German Einfluss (“influence”), Danish indflydelse (“influence”), Swedish inflytande (“influence”), Norwegian innflytelse (“influence”).
Etymology from Wiktionary, CC BY-SA 4.0.