"A trademark, trade mark, or trade-mark is a recognizable sign, design or expression which identifies products or services of a particular source from those of others. "
So a WORD itself can't be "trademarked"...
Here you can search the registrated trademarks.
--> select: "Basic Word Mark Search (New User)"
--> then select the option "Live", write the searched word (here: "airbag") and press the search button