Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
per-cōpĭōsus, a, um, adj., very abundantly supplied; hence, very rich in expression, very copious, Plin. Ep. 9, 31, 1; Sid. Ep. 1, 1.
Adv.: percōpĭōsē, very copiously, Sid. Ep. 4, 7 fin.