1.Lit. to bite down on one's tongue by accident. Ouch! I bit my tongue!
2.Fig. to struggle not to say something that you really want to say. I had to bite my tongue to keep from telling her what I really thought.I sat through that whole silly conversation biting my tongue.
to stop yourself from saying something because it would be better not to, even if you would like to say it I really wanted to tell her what I thought of him but I had to bite my tongue.