diff --git a/changelogs/internal/newsfragments/2189.clarification b/changelogs/internal/newsfragments/2189.clarification
new file mode 100644
index 00000000..f1dc9ec4
--- /dev/null
+++ b/changelogs/internal/newsfragments/2189.clarification
@@ -0,0 +1 @@
+Specify a correct spelling for "display name".
diff --git a/meta/documentation_style.rst b/meta/documentation_style.rst
index 1844f6ec..36c8d6c2 100644
--- a/meta/documentation_style.rst
+++ b/meta/documentation_style.rst
@@ -60,6 +60,11 @@ General
      you have at home. "identity server" is clear, whereas "identityserver" is
      horrible.
 
+* When talking about a user's "display name", it is spelt as two words. In
+  identifiers such as within the content of an `m.room.member` event, it is
+  spelt as a single word, `displayname`. (There are some historical exceptions
+  to this where the identifier is spelt `display_name`.)
+
 * Lists should:
 
   * Be introduced with a colon.