つけ

In a sentence

• 電気をつけてください。

  Please turn on the light.

  Here, "つけ" (tsuke) is used as the imperative form of the verb "つける" (tsukeru), which means "to turn on" or "to attach."

• 気をつけないといけません。

  You need to be careful.

  In this sentence, the phrase "気をつけ" (ki wo tsuke) is derived from "気をつける" (ki wo tsukeru), meaning "to be careful" or "to pay attention to."

• 日記をつける習慣があります。

  I have a habit of keeping a diary.

  Here, "つける" (tsukeru) means "to keep" or "to maintain" as in maintaining a habit or routine of writing.