Use the 'Copy' command to make a duplicate of one or more number of the term(s) within the tree view of thesaurus structure.
To copy the term(s):
Select the terms you want to duplicate them.
Click on the Copy button in the Edit group of the Home ribbon tab page, or press Ctrl+C.
Select the destination node. This node will be the broader term of the duplicating term(s).
Click on the Paste button in the View group of the Home ribbon tab page, or press Ctrl+V.
Wait while copying process.
In step 4, you can Click on the triangle below the Paste button and select 'Paste As Synonym' item. So, all the coping terms will be added to the synonym field of the destination term; or if you select 'Paste As Related Term' or 'Paste As Opposite', moving terms will be added to the related terms or opposites of the current focused term.
Notice: If one or more of the copied terms is put as the narrower term of the same term, you will be notified by a warning message.