Borrowing a word and changing its meaning - e.g. Russian запомнить (zapomnit') - "to remember" sounds a lot like Polish zapomnieć - "to forget".
Creating a different word, but with the same idea - e.g. Slovakian vlak (train) a Polish pociąg (train). To a Polish person these two words sound as if the former was derived from wlec (to drag) and the latter from ciągnąć (to pull).
I spent two weeks in Ukraine and once I learned the alphabet, signs were mostly intelligible, even though some familiarly sounding words had a different meaning.