A mental warm-up.

What is the meaning of the answer "sultan" in question 21? oO Because of this question, I completely stopped trying to guess further. I did a complete search of all units. I guessed monks (!). I didn't get confirmation that this was the correct answer. Instead, I got a hint that the name is slang. I did a complete search of all units again. I completely ruined my mood. :( Although now I see that among the unguessable ones were masterpieces... 1, 2, 25 are the coolest.