Lewis & Short

ap-prŏbus (adp-), a, um, adj. [ad intens.; cf. apprimus], very good or excellent; as an adj. once: adulescens adprobus, Caecil. ap. Gell. 7, 7, 9.
Once as adv.: ap-prŏbē: ni me ille et ego illum novissem adprobe, very well, Plaut. Trin. 4, 2, 117.