Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rē̆trōgrădus, a, um (collat. form rē̆-trōgrădis, e, App. M. 4, p. 151), adj. [retrogradior], going back or backwards, retrograde; usually of the stars, Sen. Q. N. 7, 25; Plin. 2, 17, 15, § 77; Sid. Ep. 8, 11: carmen retrogradum (i. e. reciprocum), Aug. Civ. Dei, 17, 15: retrogradis fuga, App. l. l.