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# keystone

«keystone» in Mova's school dictionary: **the central wedge-shaped stone at the top of an arch that…** — its meaning for a pupil, its sense in the lessons and examples, with 1 sentence of Mova's corpora that use it.

### part of speech

noun (a keystone, keystones); adjective (keystone — as in «keystone species»)

### meaning for a pupil

1) A keystone is the central wedge-shaped stone at the top of an arch that holds all the other stones in place. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#m1)

2) A keystone is the most important part of a plan, idea or system, which everything else depends on. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#m2)

3) (science) A keystone species is an animal or plant that its whole ecosystem depends on, like sea otters or beavers. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#m3)

### sense in the lessons

In history and design lessons, Roman bridges and church arches stand because of the keystone. In science lessons about food webs, removing a keystone species makes the ecosystem change greatly. Pennsylvania is called «the Keystone State». Phrases: «keystone species», «the keystone of».

### examples

- The keystone at the top holds the whole arch together. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x1)
- When the builders put in the keystone, they could remove the wooden frame. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x2)
- Sea otters are a keystone species because they eat sea urchins that destroy kelp forests. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x3)
- Reading is the keystone of learning. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x4)
- Beavers are a keystone species that build dams and make ponds. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x5)
- Pennsylvania is known as the Keystone State. [tree →](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x6)

### note

Countable. In an arch, the keystone is pushed from both sides, which locks it in; this is why arches carry heavy loads. «Keystone» is not the same as «cornerstone» (a stone at the corner of a building), though both can mean «the most important part».

### In the corpora

- [An animal that keeps a whole habitat in balance, like the sea otter, is called a keystone species.](https://md.mova.elamur.ai/free/en/corpora/school/biology/100-sea-lions-seals-and-otters/14/)

### Trees and pragmatics

[Every meaning and example of «keystone» parsed by Mova](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/), each sentence with its dependency tree and frames.