The Japanese word for mountain is
山

やま - yama

Japanese Definition

mountain
1. 名詞. （高い）山やま。（頂上付近が雪や岩で、植物がはえていないようなものを言う。）
2. 名詞. 大量のもの。
There's still a mountain of work to do.
まだ、やらなければいけない仕事が、山のように残っている。

山
1. n. a mountain (large mass of earth and rock) or (large) hill
2. n. a mine (excavation usually consisting of small tunnels)
3. n. a heap, pile
4. n. the top or high part of an object
(ja-x, ねじ山, ねじやま, thread of a screw, inline=1)
(ja-x, 帽%子の山, ぼう%しのやま, crown of a hat, inline=1)
5. n. a climax, peak
6. n. a chance, gamble
7. n. a guess, speculation
8. n. a crime, criminal case
9. n. mountain climbing, mountaineering
10. n. (colloquial) (Mount Hiei) and/or w, Enryaku-ji
11. n. (mahjong) a wall, wall tile
12. n. (informal) the △ symbol as used to mark what needs to be reviewed in study
やまを張る - to mark what needs to be reviewed
はった山が当たった。 - My selection of what I needed to review for the test was correct.
13. prefix. (prefix for species that are wild or residing in mountains)
14. counter. (counter for number of stock rise and fall like a mountain) (rfv-sense, ja)
15. counter. (counter for number of mountains, forests and/or mines)
16. suffix. Mount, Mt.
17. suffix. suffix for names of mountains
18. suffix. suffix for a temple's honorific mountain name (山号)
19. affix. mountain
20. affix. mine
21. affix. temple, temple ground
22. n. (historical Ancient Korea) mountain, hill
(synonyms, ja, 山, tr1=yama, t1=mountain, q1=general term, 丘, tr2=oka, t2=hill, q2=general term)