If the definition is flexible depending on time, culture, etc... then it is not the responsibility or the prevue of any group to "define" it. Why do the Christians get to define it? Why not the Hindus? Why not people who are neutral like atheists?
You agree it is a contract dealing with property, power of attorney, etc... Then it should apply to any two, or more, people that voluntarily agree to collectively own property. As Ron Paul says, any voluntary association or contract must be respected. Anything else is tyranny.
"In the beginning of a change the patriot is a scarce man, and brave, and hated and scorned. When his cause succeeds, the timid join him, for then it costs nothing to be a patriot."--Mark Twain