rainstorm UK /ˈɹeɪnstɔːm/US /ˈɹeɪnstɔɹm/ noun1 •A storm characterized by substantial, heavy rainfall.To make matters worse, we pass through a torrential rainstorm, which makes window-gazing almost impossible, leaving me glad that the trip is less than 30 minutes duration. — 2022 formsrainstorms