From Longman Dictionary of Contemporary Englishfirst languageˌfirst ˈlanguage noun [countable] SLthe language that you first learn as a child SYN native language/tongue, mother tongue, → second language
Examples from the Corpus
first language• It follows that an individual's patterns of thought are conditioned by the nature of his or her first language.• It was my first language, then Sincthi.• Given fluent processing of first language material, the articulatory loop may never consciously intrude into the interpreter's performance.• In this respect learner errors which reveal first language influence are the natural reflex of procedures of meaning negotiation.• Under certain circumstances, however, children may learn a pidgin as their first language. 