The definition of satem is being of a group of particular Indo-European languages.(adjective)
An example of something satem is the Armenian language.
See satem in Webster's New World College Dictionary
Origin: < Avestan satəm, hundred < Sans sátám: see hundred): so named because the initial sound illustrates the typical development in this group of the IE palatal stop, which in the centum group is a velar stop
See satem in American Heritage Dictionary 4
Origin: Avestan satəm, hundred (a word whose initial sound illustrates the change); see dekm̥ in Indo-European roots.