You have a Microsoft 365 E5 tenant.

To add a new keyword dictionary in Microsoft Purview Data Loss Prevention (DLP), you must create a Sensitive Information Type (SIT).

Sensitive Info Types (SITs) allow you to define custom detection rules, including keyword dictionaries, regular expressions, and functions for identifying sensitive content in emails, documents, and other Microsoft 365 locations. A keyword dictionary is a list of predefined words/phrases that Microsoft Purview can use to identify and classify content for DLP policies.

Steps to add a keyword dictionary:

1. Go to Microsoft Purview compliance portal

2. Navigate to Data classification > Sensitive info types

3. Create a new sensitive info type

4. Add a keyword dictionary

5. Save and use it in a DLP policy