on the killing axe, they would hit the animal to be slaughtered on the head with the hammer head, which I think they called the "pole".
The traditional spelling of the heavy back side of an axe is "poll."
...which got me interested in the etymology, which led me to the online dictionary, where I found out that the word used to mean the part of the head on which hair grows and/or the back of the head, with the origin being "polle" from middle English, meaning head or hair of the head, derived from Middle Low German, where it meant hair. So "poll" as in axe means the back of the axe head; while "poll" as in political poll probably is derived from the notion of "counting heads" favoring one side or the other of a question.
I believe the older European design of axe, formed by bending iron around a form, so that there was no heavy part, is referred to as "poll-less" by axe folks. Or something like. Modern remake of a medieval axe: