yes they are synonyms in a way. All mean something secret. Tajemnica also means mystery, and things you cannot reveal. Tajnik is a secret knowledge of a trade.
Thanks, it conflicts with what we used as children, being offspring of semi educated peasants, four years of half a day, they often used inappropriate terms. One reason I enjoy this lesson mastery of a great language.
I heard wiem and it called for znam, both mean pretty much the same but why say one when the other is called for