だんだん
Usage
だんだん is used to indicate that a state changes gradually. Thus, it often occurs with -ていく, -てくる and -くなる, -になる, -ようになる. "Gradually, little by little, bit by bit"
Examples
毎日日本語で話すようにしていると、だんだん上手に話せるようになりましすよ。
Every day I try to speak Japanese, so I gradually become better at being able to talk Japanese
春になって、だんだん暖かくなってきた。
When it becomes summer, it gradually becomes hotter.