Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
per-disco, dĭdĭci, 3, v. a., to learn thoroughly or completely, to get by heart (rare but class.): omnia jura belli, Cic. Balb. 20, 47: locus de moribus est oratori perdiscendus, id. de Or. 1, 15, 69: hominis speciem pingere, id. ib. 2, 16, 69: ad perdiscendum, Plaut. Truc. 1, 1, 1; cf. Cic. de Or. 3, 36, 147; id. Fam. 7, 14, 2 al.; Tib. 1, 10 (9), 65.
With object-clause: perdidici, isthaec esse vera, Plaut. As. 1, 3, 35.