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# keystone

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

«keystone» in the English dictionary: everyday — its meanings, how the lessons use it, and examples, each with its tree on Mova.

## Everyday

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://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://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://mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#m3)

### 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://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://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://mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x3)
- Reading is the keystone of learning. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x4)
- Beavers are a keystone species that build dams and make ponds. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/#x5)
- Pennsylvania is known as the Keystone State. [tree →](https://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».

## On Mova

- [Trees and pragmatics of «keystone» in the school dictionary](https://mova.elamur.ai/free/en/corpora/dictionaries/school/K/keystone/): every meaning and example parsed by Mova, with its dependency tree and frames.
- [«keystone» in the school dictionary](https://mova.elamur.ai/free/en/dictionaries/school/w/keystone.html) on Mova free.