Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sŭpīno, āvi, ātum, 1, v. a. [supinus], to bend or lay backwards, to place, put, or throw a person or thing on the back (poet. and in post-Aug. prose): manus modice supinata, Quint. 11, 3, 100; 11, 3, 119: supinata testudo, Sen. Ep. 121, 9: miles supinatus humi, App. M. 9, p. 236; 8, p. 211, 7: aliquem in terga, Stat. Th. 6, 789: equi equitem supinant, id. ib. 8, 394: corpora prona supinat (regina), id. ib. 12, 290: currum temone erecto, id. ib. 3, 414: ante supinatas Aquiloni ostendere glebas, turned over, ploughed up, Verg. G. 2, 261: Parnason tauris, Stat. Th. 7, 347: nasum nidore supinor, I turn up my nose, Hor. S. 2, 7, 38: supinari, to lie along, extend, Stat. Th. 12, 243: arcus supinatus, bent, Manil. 2, 852 (but in Sen. Ben. 2, 13, 2, the correct read. is resupinet).