noun
the language that you learn to speak first as a child; the language that you speak best :
His first language is Welsh.
—compare second language
noun
the language that you learn to speak first as a child; the language that you speak best :
His first language is Welsh.
—compare second language
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005