What is the X in X-mas?
1640s, Modern Latin, from Greek idiopatheia, from comb. form of idios "one's own" (see idiom) + -patheia, comb. form of pathos "suffering, disease, feeling" (see pathos). Related: idiopathic.
idiopathy id·i·op·a·thy (ĭd'ē-ŏp'ə-thē)n.
A disease of unknown origin or cause.
A primary disease arising spontaneously with no apparent external cause.