Something put forward to be accepted or refused. A proposal is not a decision — it is the asking.
Latin proponere (to set forth, to display, to propose): pro- (forward) + ponere (to place); a proposal places something in front of others without placing it into effect.
Something placed forward to be accepted or refused, and not yet a decision. The root's placing is provisional by nature — to propose is to set a thing where it can be seen, not where it is fixed.