At a gemara Shiur, I often heard the expression "it is peley" and the word "navamina". I do not know what these words mean. Navamina is not in the Melamed Dictionnary... Can you please tell me the meaning of these words / expressions ?
I'm not sure what you mean by "peley", but I imagine that the phrase you are hearing as "navamina" is actually "hava amina," which means "what one would have thought". For example, the Gemara might state a fact that seems obvious, and the person leading the shiur might ask, "What's the hava amina?" In other words, why did the gemara have to say that? What else would I have thought?
It doesn't have to be used in that negative context, though. You could also say, "If the mishna hadn't said that, the hava amina would have been X. Now that we know Y, we know X is not true and in fact, Z is true."
It occurred to me that instead of "hava amina" you might have actually been mishearing the expression "nafka mina", which means practical difference. For example, two amoraim could be arguing about the reason for some halacha and the gemara could ask "Mai nafka mina?" Meaning, what practical difference in the practice of the halacha would we observe depending on which amorah is correct? The gemara then goes on to answer how the difference in reason for the din could actually affect what the halacha is in some particular scenario.
The word "peley" is probably פלא, which means it is a "wonder" or something amazing or incredible. It often refers to something being very surprising in its novelty.
I assume Daniel is correct about "navamina"