Unfortunately you can not do that in Polish language. You have to understand that in Polish language each word can have person inflection and <b>7 case inflection</b>. When you could say for example "turtle" and use it in every sentence in English, in Polish you wouldn't just have "żółw". It would be: "żółw", "żółwia", "żółwiowi", "żółwia" (same as second but used in different sentence and situation), "żółwiem", "żółwiu", "żółwiu" (same as previous but again different usage). And that's only in singular form (don't get me even started on the plural form :)). 

So while I understand that you would like to have a uniform name for that it is just not going to happen in Polish language.