Perhaps you should try some spelling variations:
"trade unionist" » "trade unionists", "trades unionist", "trades unionism", "trade unionsist", "trade unitedist"
"trade unionism" » "trade unions", "trades unions", "trade unionsism", "trade unitedism"
"trade union" » "trade unions", "trade united"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("trade unionist") OR ((("trade unionism") OR ("trade union")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"trade unionist\") or (((\"trade unionism\") OR (\"trade union\"))))".
• Removing quotes may allow a broader search: (( trade unionist ) or ((( trade unionism ) OR ( trade union )))).
• Adding a wildcard symbol may retrieve word variants: (("trade unionist") or ((("trade unionism") OR ("trade union"))))*.