κόλασιν [1 verse](noun sg fem acc) "Punishment" is from kolasis, which primarily means "checking the growth of trees," and from that idea, "chastisement" and "correction." This is the only time this word is used in the Gospels. - The word translated as "punishment" means the pruning of trees. From there, you get the meaning of "curb" and "restrain", stopping a certain behavior, so, "chastisement." The idea of "punish" is a bit of a reach. In the context of the theme of productivity, which is hidden in much of this chapter, including in the words translated as 'do" in the previous verse, Matthew 25:45, the term is well chosen. Trees (like fields) are Christ's symbols for the productivity of existing assets. The idea of pruning fits well with the fire of the trash heap in that verse as well.