IPA: /ˈreɪnˌstɔːm/
KK: /ˈreɪnˌstɔrm/
A type of storm that brings heavy rain and often strong winds.
The rainstorm caused flooding in the streets.
Rainstorm → It is formed from "rain" (from Old English *regn*, meaning water droplets falling from the sky) and "storm" (from Old English *storm*, meaning a disturbance in the atmosphere). The word "rainstorm" refers to a storm characterized by heavy rain.
Think of 'water droplets falling from the sky' ('rain') combined with a 'disturbance in the atmosphere' ('storm') — that's what a rainstorm is.