Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mŏnŏlĭthus, a, um, adj., = μονόλιθος, consisting of a single stone, monolith (ante- and post-class.): columnae, Laber. ap. Non. 544, 33: postes marmorei monolithi, Ampel. Lib. Mem. 8, 12; Inscr. Orell. 1593.