No. 10No. 10 /ˌnʌmbə ˈten $ -bər-/PGO (No. 10 Downing Street) the address of the officialhome of the BritishPrimeMinisterFrom Longman Business DictionaryNo. 10No. 10 /ˌnʌmbə ˈten-bər-/ noun journalismNumber 10 Downing Street in London; the official home of the British prime minister, and used to talk generally about his or her decisions and activitiesAn announcement from No. 10 is expected later today.