What is the X in X-mas?
1834, introduced by English physicist and chemist Michael Faraday (suggested by the Rev. William Whewell, English polymath), coined from Greek ion, neuter present participle of ienai "go," from PIE root *ei- "to go, to walk" (cf. Greek eimi "I go;" Latin ire "to go," iter "a way;" Old Irish ethaim "I go;" Irish bothar "a road" (from *bou-itro- "cows' way"), Gaulish eimu "we go," Gothic iddja "went," Sanskrit e'ti "goes," imas "we go," ayanam "a going, way;" Avestan ae'iti "goes;" Old Persian aitiy "goes;" Lithuanian eiti "to go;" Old Church Slavonic iti "go;" Bulgarian ida "I go;" Russian idti "to go"). So called because ions move toward the electrode of opposite charge.
suffix forming nouns of state, condition, or action from verbs, from Latin -ionem (nominative -io), sometimes via French -ion.
ion i·on (ī'ən, ī'ŏn')
An atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons.