How could I translate "一语道破", "一语道破天机" I want translate "一语道破" or "一语道破天机" to a phase with an etymology.

tell the truth, blurts out the whole truth, 

seem not very good.
i would suggest "freudian slip"

if it's fate, destiny related, maybe "oracle slip", or "divine slip"

in which slip referred to the "一語"

have fun :)