centum vs satem languages [Lat. centum, Skt śatám ‘one hundred’]
In historical linguistics, a division set up according to the reconstruction of the Indo-European languages into a Western and an Eastern group that are named after their respective term for the numeral ‘100.’ The original (now not uncontroversial) thesis maintained the following: The Indo-European proto-language had three series of guttural sounds, i.e.
velars [k, g, gh], palatals [k’, g’, gh’] and labio-velars . These three rows were developed differently in the individual daughter languages: in the so-called centum languages (= Germanic, Celtic, Italic, etc.) the palatals merged with the velars, the labio-velars remaining separate; in the so-called satem languages (=Indic (Indo-Aryan), Iranian, Slavic, etc.) the velars merged with the labio-velars, while the palatals here remained separate and subsequently developed further into spirants. Consequently, the originally palatal stop corresponds to [k] in centum languages (in Germanic to [h] due to subsequent Grimm’s law) and to some kind of sibilant in the satem languages. Several criticisms of a phonological kind have been leveled against this hypothesis; but especially the more recent discoveries of Tocharian (1904) and Hittite (1906), two centum languages located in the east, have proved this classification into two geographically and phonologically distinguished language branches to be not unproblematic; also, the development within the individual languages is not as unequivocal as was formerly believed.
. These three rows were developed differently in the individual daughter languages: in the so-called centum languages (= 
