What is the X in X-mas?
Old English geoguð "youth," related to geong "young," from West Germanic *jugunthiz (cf. Old Saxon juguth, Old Frisian jogethe, Middle Dutch joghet, Dutch jeugd, Old High German jugund, German Jugend, Gothic junda "youth"), from the source of young (adj.)) + Proto-Germanic abstract noun suffix *-itho (see -th (2)).
The West-Germanic form was altered from Proto-Germanic *juwunthiz by influence of its contrast, *dugunthiz "ability" (source of Old English duguð). In Middle English, the medial -g- became a yogh, which then disappeared.
They said that age was truth, and that the young
Marred with wild hopes the peace of slavery