What is the X in X-mas?
late 15c., from Middle French confluent or directly from Latin confluentem (nominative confluens), present participle of confluere "to flow together" (see confluence). The noun meaning "a stream which flows into another" is from 1850.
confluent con·flu·ent (kŏn'flōō-ənt)
Flowing together; blended into one.
Merging or running together so as to form a mass, as sores in a rash.