Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sēmĭ-līber, ĕra, ĕrum, adj., half-free: semiliberi saltem simus, Cic. Att. 13, 31, 3; id. ap. Sen. Brev. Vit. 5, 2.