Po·la·ris1 /pəˈlɑːrɪs $ -ˈlæ-/ a ballistic missile (=a flying weapon) fired from a submarine, which was developed in the US in the 1950s and 1960s and is a nuclear weapon. Polaris missiles were kept by the military forces of the US and the UK until the 1990s, when they were replaced by Trident missiles.