bpo-33957: Doc: Use better wording (GH-7912)

Doc/faq/design.rst

@@ -500,7 +500,7 @@ on the key and a per-process seed; for example, "Python" could hash to
 to 1142331976.  The hash code is then used to calculate a location in an
 internal array where the value will be stored.  Assuming that you're storing
 keys that all have different hash values, this means that dictionaries take
-constant time -- O(1), in computer science notation -- to retrieve a key.
+constant time -- O(1), in Big-O notation -- to retrieve a key.
 
 
 Why must dictionary keys be immutable?