pickknuckle under knuckle under {v. phr.} To do something because you are forced to do it. Bobby refused to knuckle under to the bully. Compare: GIVE IN. Categories: add yours verb Source: A Dictionary of American Idioms 'knuckle under' on video English Tutor Nick P Verb Phrase (233) Knuckle Under Knuckle Under Knuckle Under Shooting my Bernie's knuckle under sort: relevance, mode: exact match, q: "knuckle under", maxResults: 4, videoEmbeddable: true, videoSyndicated: true, safeSearch: strict, type: video Subscribe to: American IdiomsEnglish Slang Add my comment