Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† măthēsis, is (with the second syll. short: involvit măthĕsi, Prud. adv. Symm. 2, 893 al.; Sid. Carm. 5, 131), f., = μάθησις (lit., knowledge, science; hence, in partic.).