There is the difference but only in ancient Hebrew

The words שקר and כזב are the same. שקר is more common and usually you'll find the word כזב in books or in more official cases.

Thanks Jarden, this is very useful

There is obviously a big difference between biblical and modern meaning of the same word.. What I can think of , is that כזב is more like a pre meditated lie , more like a made up story . Anyway when we use it (for that emphasis) we use the two synonym combined . Example : "זה שקר וכזב" meaning it's totally false . Other small hint of the word's origin is maybr its root כ.ז.ב. . אכזבה = Dissappointment לאכזב = to dissappint. Other standalone terms : נחל אכזב is a water creek which has become dry empty of water and is no longer an active stream. אהבה נכזבת is Lost love , the bad experience of a love story that tragiclly failed or one within someone was turned down. And, As far as I know, the noun כזב is not used in a verb form. Unlike שקר .