#centumsatem split
The words for ‘one hundred’ in Indo-European languages exemplify an ancient sound change – the centum/satem split (the Latin and Avestan words for ‘one hundred’ respectively).
Proto-Indo-European has been reconstructed as having three ‘series’ of velar consonants – palatal velars, plain velars and labiovelars (*kj, *k and *kw respectively). However, in nearly all daughter languages, these three series collapsed into two. Languages on the centum-side of the split merged the palatal and plain series to be left with *k and *kw and those on the satem-side merged the labiovelars and plain series to give *kj and *k.
It was thought to be the case that the centum/satem split represented an ancient dialect division of Indo-European languages. Most centum-languages are found in the west whilst most satem-languages are found in the east. However, a number of problems with this view exist. Tocharian is a centum-language but is (or was) the furthest east of any Indo-European language. There is also evidence that some languages kept the three series distinct in certain environments longer than others, e.g. Luvian (an extinct IE language spoken in Anatolia).
This, plus other evidence, suggests that the centum/satem labels are better viewed as descriptive shorthands which are used to label mergers which occurred independently in various Indo-European daughter languages (although this view raises problems of its own as well!).
