What is the X in X-mas?
1650s, "practice of representing things with symbols," from symbol + -ism. Attested from 1892 as a movement in French literature that aimed at representing ideas and emotions by indirect suggestion rather than direct expression; rejecting realism and naturalism, it attached symbolic meaning to certain objects, words, etc. French symboliste was coined by poet Paul Verlaine (1844-1896) in 1885.
symbolism sym·bol·ism (sĭm'bə-lĭz'əm)
A mental state in which everything that happens is regarded by the individual as symbolic of his or her own thoughts.
The disguised representation in conscious thought of unconscious or repressed contents or events.