diff --git a/README.rst b/README.rst
index ebf5158..025707a 100644
--- a/README.rst
+++ b/README.rst
@@ -70,6 +70,14 @@ ordered list of known fallback names. If an API consumer cannot find a given
 list of ``aliases`` here, in the order they are given, in order to find
 the requested endpoint.
 
+secondary (optional)
+--------------------
+
+If secondary is set and is true, the project is not the primary service people
+associate with the project codename. For instance, the ``nova`` project has
+two services, ``compute`` and ``placement``. ``compute`` is the primary
+project. ``placement`` is secondary.
+
 Naming
 ======
 
diff --git a/schema.json b/schema.json
index f705e41..d97da75 100644
--- a/schema.json
+++ b/schema.json
@@ -44,6 +44,10 @@
                  "type": "string"
                },
                "description": "An ordered list of historical aliases for this service type."
+            },
+            "secondary": {
+                "type": "boolean",
+                "description": "Is this a secondary service for a project?"
             }
          },
          "additionalProperties":false,