This is the 565th most frequent German word.
fällen
"Fällen" means "to fell" or "to cut down" (e.g., a tree).
Here, 'fällen' means 'to cut down' as applied to trees or physical objects.
Der Förster muss einen Baum fällen.
The forester must fell a tree.
In this usage, 'fällen' metaphorically means 'to decide upon' or 'to pass a legal judgment'.
Das Gericht wird ein Urteil fällen.
The court will pass a judgment.
In this sentence, 'fällen' extends to decision-making, conveying the act of making a choice or decision.