Linguistic reconstruction is the practice of establishing the features of an unattested ancestor language of one or more given languages. There are two kinds of reconstruction. Internal reconstruction uses irregularities in a single language to make inferences about an earlier stage of that language – that is, it is based on evidence from that language alone. Comparative reconstruction, usually referred to just as reconstruction, establishes features of the ancestor of two or more related languages, belonging to the same language family, by means of the comparative method. A language reconstructed in this way is often referred to as a proto-language (the common ancestor of all the languages in a given family); examples include Proto-Indo-European, Proto-Dravidian, etc.
In texts concerning linguistic reconstruction, reconstructed forms are commonly prefaced with an asterisk (*), to distinguish them from attested forms.
An attested word from which a root in the proto-language is reconstructed is a reflex. More generally, a reflex is the known derivative of an earlier form, which may be either attested or reconstructed. Reflexes of the same source are cognates.
Anthony Fox, Linguistic Reconstruction: An Introduction to Theory and Method (Oxford University Press, 1995) ISBN 0-19-870001-6.
Henry M. Hoenigswald, Language Change and Linguistic Reconstruction (University of Chicago Press, 1960) ISBN 0-226-34741-9.