The suffix -en attaches to words to create verbs that mean “to make” or “to become.” When you darken a room, you make it dark. When storm clouds darken the sky, they become dark. The suffix works both ways, depending on context.

You see -en everywhere once you start noticing it. Strengthen means to make or become strong. Soften means to make or become soft. Lengthen, widen, deepen, brighten, loosen, and tighten all follow the same pattern. The suffix turns descriptive words into action words.

Sometimes en- appears at the beginning of words too, like enable (to make able) or enlarge (to make large), though these use the prefix en- rather than the suffix -en.

It's one of those small but powerful word-building tools that lets us create exactly the verb we need. Instead of saying “make it tight,” we simply say tighten. Instead of “cause to be sweet,” we say sweeten.

Notice that -en verbs often describe gradual processes: the sky darkens slowly at sunset, bread dough softens as it rises, your muscles strengthen over weeks of practice.