semi-solid UK /ˌsɛm.iːˈsɒl.ɪd/US /ˌsɛm.iˈsɔl.ɪd/adjective 1noun 1forms 3 adjective1 •Half-solid, extremely viscous. noun1 •Synonym of quasi-solid. formssemi-solids · more semi-solid · most semi-solid