1.NounThe digit 0 that begins all telephone numbers in the United Kingdom, which is substituted for the country code in the event of international calls.
2.NounA prefix which is a null morpheme, used in models of linguistic analysis to represent the lack of a prefix where one might otherwise be expected (for example, as one of several inflections that a stem can take, or the reduction of a historically vocalised prefix to the point that it is inaudible).