bite one's lip - Wiktionary, the free dictionary
From Wiktionary, the free dictionary
bite one's lip (third-person singular simple present bites one's lip, present participle biting one's lip, simple past bit one's lip, past participle bitten one's lip)
- (idiomatic) To forcibly prevent oneself from speaking, especially in order to avoid saying something inappropriate or likely to cause a dispute.
1822, [Walter Scott], chapter XIII, in Peveril of the Peak. […], volume IV, Edinburgh: […] Archibald Constable and Co.; London: Hurst, Robinson, and Co., →OCLC, page 304:
Buckingham bit his lip, for he saw the introduction of Lady Derby was likely to confuse and embroil every preparation which he had arranged for his defence; […]