is an adverb that is used to express the slight, but constant, progression of something. Originally, it comes from the kanji construction 段々（だんだん）
, which can be thought of as meaning ‘step by step’, ‘stepwise’, or even ‘steadily’. だんだん
is similar to ほとんど
, in that it can modify the meaning of entire phrases, rather than just single words.
To use だんだん
, simply put it before the phrase that you want to express as ‘(A) that is increasing steadily’.
Since December, it has gotten colder steadily.
I have steadily gotten used to work’s environment.
can take the particle と
, it is not required. In fact, と
is very often omitted from adverbs/onomatopoeic words (words that represent a sound or motion) in Japanese.
Initially, it can be easy to mix-up だんだん
, with どんどん
is an onomatopoeic word that represents loud banging (like on a drum), so is used to express fast changes/progression. This is unlike だんだん
, which expresses slower changes/progression.
It is starting to rain. (Slow progression, does not imply great speed or severity)
It is starting to rain. (Rapid progression, may imply great speed and/or severity)