Centum is the collective name for the branches of Indo-European in which the so-called Satem shift, the change of palato-velar *k^, *g^, *g^h into fricatives or affricates, did not take place, and the palato-velar consonants merged with plain velars (*k, *g, *gh). Most of the Centum languages preserve Proto-Indo-European labio-velars (*kw, *gw, *gwh) or their historical reflexes as distinct from plain velars; for example, PIE *k, *kw > Latin c /k/, qu /kw/, Greek /k/, /p/ (or /t/ before front vowels), Gothic /h/, /hw/, etc.
The name Centum comes from the Latin word centum '100', pronounced [kentum] < PIE *k^mtom, illustrating the falling together of *k and *k^. Compare Sanskrit s′ata- or Russian sto, in which *k^ changed into a fricative.
The Centum branches include Anatolian, Tocharian, Italic, Celtic, Germanic, Greek, and a number of minor and little known extinct groups (such as Venetic and the ancient Macedonian language and probably the Illyrian languages).
The Centum group is a paraphyletic group and thus not a phylogenetic unit.
