Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
clāthro (in MSS. also clātro), no perf., ātum, 1, v. a. [clathri], to furnish with a grate or lattice, to set with bars (very rare), Cato, R. R. 4; Plaut. Mil. 2, 4, 26; Col. 9, 1, 4; Inscr. Grut. 207, 2.