speech impediment
From Longman Dictionary of Contemporary Englishspeech impedimentˈspeech imˌpediment noun [countable] a physical or nervous problem that affects your speechExamples from the Corpusspeech impediment• He had a nervous twitch and a speech impediment.• He also had a speech impediment.• A speech impediment did nothing to stop him from preaching.• I kept silent, thinking that he might have an embarrassing speech impediment.