retrogress

n. [ Cf. F. rétrogression. See Retrograde, and cf. Digression. ] 1. The act of retrograding, or going backward; retrogradation. [ 1913 Webster ]

2. (Biol.) Backward development; a passing from a higher to a lower state of organization or structure, as when an animal, approaching maturity, becomes less highly organized than would be expected from its earlier stages or known relationship. Called also retrograde development, and regressive metamorphism. [ 1913 Webster ]

a. [ Cf. F. rétrogressif. ] 1. Tending to retrograde; going or moving backward; declining from a better to a worse state. [ 1913 Webster ]

2. (Biol.) Passing from a higher to a lower condition; declining from a more perfect state of organization; regressive. [ 1913 Webster ]