WordWeb Online

1. Rain heavily
   "Put on your rain coat-- it's pissing down outside!";
   - pour, pelt, rain cats and dogs [informal], rain buckets [informal], belt down [informal], pelt down [informal], tip [Brit, informal], chuck it down [Brit, informal], chuck [Brit, informal], bucket [Brit, informal], teem [informal]

Derived forms: pissing down, pisses down, pissed down

Type of: rain, rain down