diff -u b/core/lib/Drupal/Core/Entity/EntityType.php b/core/lib/Drupal/Core/Entity/EntityType.php
--- b/core/lib/Drupal/Core/Entity/EntityType.php
+++ b/core/lib/Drupal/Core/Entity/EntityType.php
@@ -205,23 +205,23 @@
    *   An array of values from the annotation.
    */
   public function __construct($definition) {
-    foreach ($definition as $key => $value) {
-      $this->{$key} = $value;
+    foreach ($definition as $property => $value) {
+      $this->{$property} = $value;
     }
   }
 
   /**
    * {@inheritdoc}
    */
-  public function get($key) {
-    return isset($this->{$key}) ? $this->{$key} : NULL;
+  public function get($property) {
+    return isset($this->{$property}) ? $this->{$property} : NULL;
   }
 
   /**
    * {@inheritdoc}
    */
-  public function set($key, $value) {
-    $this->{$key} = $value;
+  public function set($property, $value) {
+    $this->{$property} = $value;
     return $this;
   }
 
diff -u b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
--- b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityTypeInterface.php
@@ -13,38 +13,27 @@
 interface EntityTypeInterface {
 
   /**
-   * Gets any arbitrary key.
+   * Gets any arbitrary property.
    *
-   * @param string $key
-   *   The key to retrieve.
+   * @param string $property
+   *   The property to retrieve.
    *
    * @return mixed
-   *   The value for that key, or NULL if the key did not exist.
+   *   The value for that property, or NULL if the property does not exist.
    */
-  public function get($key);
+  public function get($property);
 
   /**
-   * Sets a value to an arbitrary key.
+   * Sets a value to an arbitrary property.
    *
-   * @param string $key
-   *   The key to use for the value.
+   * @param string $property
+   *   The property to use for the value.
    * @param mixed $value
    *   The value to set.
    *
    * @return static
    */
-  public function set($key, $value);
-
-  /**
-   * Indicates if a given entity key exists.
-   *
-   * @param string $key
-   *   The name of the entity key to check.
-   *
-   * @return bool
-   *   TRUE if a given entity key exists, FALSE otherwise.
-   */
-  public function hasKey($key);
+  public function set($property, $value);
 
   /**
    * Returns the unique identifier of the entity type.
@@ -71,6 +60,36 @@
   public function getClass();
 
   /**
+   * Returns an array of entity keys.
+   *
+   * @return array
+   *   An array describing how the Field API can extract certain information
+   *   from objects of this entity type:
+   *   - id: The name of the property that contains the primary ID of the
+   *     entity. Every entity object passed to the Field API must have this
+   *     property and its value must be numeric.
+   *   - revision: (optional) The name of the property that contains the
+   *     revision ID of the entity. The Field API assumes that all revision IDs
+   *     are unique across all entities of a type. This entry can be omitted if
+   *     the entities of this type are not versionable.
+   *   - bundle: (optional) The name of the property that contains the bundle
+   *     name for the entity. The bundle name defines which set of fields are
+   *     attached to the entity (e.g. what nodes call "content type"). This
+   *     entry can be omitted if this entity type exposes a single bundle (such
+   *     that all entities have the same collection of fields). The name of this
+   *     single bundle will be the same as the entity type.
+   *   - label: The name of the property that contains the entity label. For
+   *     example, if the entity's label is located in $entity->subject, then
+   *     'subject' should be specified here. If complex logic is required to
+   *     build the label, a 'label_callback' should be defined instead (see the
+   *     $label_callback block above for details).
+   *   - uuid (optional): The name of the property that contains the universally
+   *     unique identifier of the entity, which is used to distinctly identify
+   *     an entity across different systems.
+   */
+  public function getKeys();
+
+  /**
    * Returns a specific entity key.
    *
    * @param string $key
@@ -84,6 +103,17 @@
   public function getKey($key);
 
   /**
+   * Indicates if a given entity key exists.
+   *
+   * @param string $key
+   *   The name of the entity key to check.
+   *
+   * @return bool
+   *   TRUE if a given entity key exists, FALSE otherwise.
+   */
+  public function hasKey($key);
+
+  /**
    * Indicates whether entities should be statically cached.
    *
    * @return bool
@@ -111,36 +141,6 @@
   public function isFieldDataCacheable();
 
   /**
-   * Returns an array of entity keys.
-   *
-   * @return array
-   *   An array describing how the Field API can extract certain information
-   *   from objects of this entity type:
-   *   - id: The name of the property that contains the primary ID of the
-   *     entity. Every entity object passed to the Field API must have this
-   *     property and its value must be numeric.
-   *   - revision: (optional) The name of the property that contains the
-   *     revision ID of the entity. The Field API assumes that all revision IDs
-   *     are unique across all entities of a type. This entry can be omitted if
-   *     the entities of this type are not versionable.
-   *   - bundle: (optional) The name of the property that contains the bundle
-   *     name for the entity. The bundle name defines which set of fields are
-   *     attached to the entity (e.g. what nodes call "content type"). This
-   *     entry can be omitted if this entity type exposes a single bundle (such
-   *     that all entities have the same collection of fields). The name of this
-   *     single bundle will be the same as the entity type.
-   *   - label: The name of the property that contains the entity label. For
-   *     example, if the entity's label is located in $entity->subject, then
-   *     'subject' should be specified here. If complex logic is required to
-   *     build the label, a 'label_callback' should be defined instead (see the
-   *     $label_callback block above for details).
-   *   - uuid (optional): The name of the property that contains the universally
-   *     unique identifier of the entity, which is used to distinctly identify
-   *     an entity across different systems.
-   */
-  public function getKeys();
-
-  /**
    * Sets the name of the entity type class.
    *
    * @param string $class