Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
possĭbĭlis, e, adj. [possum], that may exist or may be done, possible (post-Aug.): melius qui tertiam partem dixerunt δυνατόν, quod nostri possibile nominant, Quint. 3, 8, 25: condiciones, Dig. 28, 3, 16: possibile est, with subject-clause, ib. 25, 2, 3; Vulg. 2 Macc. 3, 6.
Hence, adv.: possĭ-bĭlĭter, Jul. ap. Aug. c. Sec. Resp. Jul. 2, 52.