In obsolete|lang=en terms the difference between hiation and piation
is that hiation is (obsolete) the act of gaping; a gap while piation is (obsolete) the act of making atonement; expiation.
As nouns the difference between hiation and piation
is that hiation is (obsolete) the act of gaping; a gap while piation is (obsolete) the act of making atonement; expiation.