To do wonderful or exciting things; to cause a great or remarkable sensation in the world; to be extremely exciting, popular, famous, renowned, etc. (Refers to the Thames river in London. Often used in the negative to indicate the opposite.) Primarily heard in UK. I wouldn't be too concerned with what he thinks of you. For all his money and education, he's hardly setting the Thames alight, is he?When she was a child, Janet dreamed of setting the Thames alight as a famous actress.