Language change is continuous and vital for the sociocultural adaptation and status development of language varieties. Perhaps the most important linguistic feature of Nigerian English language change is semantic extension which refers to the process whereby terms already existing in English (standard English) acquire new meanings. This paper investigated the usage of semantic extension in Nigerian English (NIE), the social motivations responsible for such semantic innovations and the relevance of linguistic innovations for the description and teaching of English in Nigeria. Using descriptive qualitative research design, data for the research were collected using naturally occurring language forms while other information sources included print and social media, educational, political and religious institutions. It was found that semantic extension in Nigerian English is rule-governed, based on culture, multilingualism, technological innovations, socio-economic experiences and indigenous conceptual framework. The data further revealed that the semantic extensions are sociolinguistically recognized by educated users of Nigerian English and linguistic norm and not mere linguistic deviation from Standard English. It was observed that semantic extension promotes lexical reduction, language creativity and the institutionalization of Nigerian English as a variety of the World Englishes paradigm. It was recommended that Nigerian English new lexical items should be incorporated into English textbooks and dictionaries, Nigerian English lexical innovations should form the basis for the teaching of English in Nigeria.