"Pancerz" can be used to describe different things: - a part of an armour or a shielding in general (for example: of a tank), - a hard layer covering (and protecting) an animal (compare with "pancernik" = "armadillo") - someone's attitude (if he/she is hiding his/her fillings) - perhaps something else... "Zbroja" is mainly used to refer to an armour of a knight.