Synonyms can be created for the following types of objects:

Assembly (CLR) Stored Procedure

Assembly (CLR) Table-valued Function

Assembly (CLR) Scalar Function

Assembly Aggregate (CLR) Aggregate Functions

Replication-filter-procedure

Extended Stored Procedure

SQL Scalar Function

SQL Table-valued Function

SQL Inline-table-valued Function

SQL Stored Procedure

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Table (User defined) - Includes local and global temporary tables