The Name of this Family:
In books and monographs written about a century ago this family of languages was designated as the Aryan family. The use of the epithet Aryan in this context has virtually been abandoned nowadays and if it is used at all, it is used to designate the Indo-Iranian branch of this family. Some scholars, German philologists in particular, designated this family as the Indo-European family and many philologists, German and non-German alike, use this term even now.
The use of the term “Indo-Germanic” or “Indo-Teutonic” seems to have been motivated by the desire to mark the two extremes of the geographical territory covered by this family of languages. “Indo” in this term was intended to indicate the eastern boundary and “Germanic” and its synonym “Teutonic” were intended to mark the western boundary of this territory.
At that time, Celtic languages, i.e., languages like Cornish and Welsh were not known to be part of the Indo-Germanic family. On the basis of the research done around the beginning of the twentieth century, it has now been more or less indisputably established that Celtic languages are an integral part of the Indo-European family and cannot be assigned to any other family of languages. Celtic languages like Cornish and Manx were used much farther in the west than English, a Germanic language.
In other words, the western limit of the geographical territory covered by this family of languages is marked not by English but by Celtic languages. It can, therefore, be argued that “Indo-Celtic” is a more appropriate label for this family. “Indo-European” is perhaps the least controversial and most widely used term these days.