influence: [14] Influence began life as an astrological term. It was coined in medieval Latin as influentia from the present participle of Latin influere ‘flow in’, a compound verb based on fluere ‘flow’, and to begin with denoted a sort of fluid that was supposed to be given off by the stars and to influence human life. English originally acquired the word with this meaning, and it was not until the end of the 16th century that the main current sense ‘power to produce effects’ started to establish itself.
The more concrete notion of an ‘emanation’ that affected people also lay behind the use of Italian influenza for ‘epidemic’, from which English got influenza (see FLU). Another English acquisition from Latin influere is influx [17], which comes from its past participle. => flu, fluent, influx
