Hmm i can tell u : a word or phrase that means exactly or nearly the same as another word or phrase in the same language ,for example: close is a synonym of shut . "the west was a SYNONYM for the ussr".
population growth: refers to the change in population over a unit time period.
population density:number of people living in a certain area at an average is callen population density.
ahhh by reading this above information you can come to a conclusion weather both are SYNONYMS or not.