くにばんごう
noun
country code (for international dialing)
communicationnumber
1. country code; international dialing code
The number dialed before a phone number to reach another country — 81 for Japan, 1 for the United States. Also used for the country code entered in online forms.
日本(にほん)国番号(くにばんごう)81だ。
Japan's country code is 81.
国番号(くにばんごう)つけて電話(でんわ)かけてください
Please dial with the country code included.
国際電話(こくさいでんわ)かけるとき最初(さいしょ)国番号(くにばんごう)入力(にゅうりょく)する必要(ひつよう)ある
When making an international call, you need to enter the country code first.
The leading zero of a mobile number is dropped when the country code is added.

The first element takes the kun'yomi くに, not the on'yomi こく — a reading trap, since most compounds written with (こく) use こく.

Common collocations

Similar words