Noun
(many) mountains
この辺の山々は変化に富んでいる。The mountains in this part of the country are full of variety. Adverb (fukushi)
very much (wanting to do something one cannot); greatly; really
Usually written using kana aloneas 〜たいのはやまやまだが..., 欲しいのはやまやまだが..., etc.
so many; a lot of
Usually written using kana alone
Also written 山山【やまやま】