adjective. Existing without a perceptible cause; spontaneous.

Having no precedent cause; existing without an author; uncreated; self-existent.

adjective. Having no antecedent cause; uncreated; self-existent; eternal.

adjective. That which happens spontaneously, unintended and uninitiated.

adjective. Since all things must come from something that causes them the uncaused cause is that one thing that began the chain of existance, often identified as God.

adjective. having no cause or apparent cause

"But, this being impossible, we must be content, wherever we stop, to contemplate the uncaused, that is, the unexplained; and then all that follows is only relatively explained."

unintended  

ahistorical  autochthonic  cogwheel  consubstantial  deep-down  

accidental  adventitious  aleatory  casual  causeless