sit in verb 3sit-in adjective 1sit-in noun 1forms 4 verb3 •To attend a class, educational presentation, meeting, etc. for one time, as a visitor. •To take part in a group musical performance, especially a jazz session, as a temporary guest. •To participate in a sit-in protest.Over 200 homeless women and children sat-in over night at the state house to protest inadequate state funding for Aid to Families with Dependent Children (AFDC). — 1987 sit-in adjective1 •Designed to be sat in. sit-in noun1 •A peaceful form of protest in which people occupy an area and refuse to leave.Thousands of students marched in the streets and staged a sit-in at T’ien-an-men Square, chanting “Long live democracy! Long live freedom! Down with corruption!” — 2000 formssat in · sitting in · sits in · sit-ins