# getParameterDefinition

> Looks up the vocabulary entry for a parameter. A cas parameter resolves through the published equivalences to its welldot entry. Returns undefined for unknown codes, CAS numbers without an equivalent, and x- vocabularies.

> **getParameterDefinition**(`parameter`): [`ParameterDefinition`](/core/api/type-aliases/ParameterDefinition) \| `undefined`

Looks up the vocabulary entry for a parameter. A `cas` parameter resolves
through the published equivalences to its `welldot` entry. Returns
`undefined` for unknown codes, CAS numbers without an equivalent, and
`x-` vocabularies.

## Parameters

### parameter

[`Parameter`](/core/api/type-aliases/Parameter)

## Returns

[`ParameterDefinition`](/core/api/type-aliases/ParameterDefinition) \| `undefined`