From rotting + -ly.
rottingly (comparative more rottingly, superlative most rottingly)
- In a rotting manner.
1846, Andrew McEwen, “The Sorrow-stricken”, in Zayda, and Other Poems[1], Belfast: […] Lamont, Brothers, […], →OCLC, page 130:The yellow leaf lies rottingly / Round a mansion’s trellised door; / Its lord hath that deep sunken eye, / Nought now can e’er restore; […]
1916, Lucas Malet (Mrs. Mary St. Leger Harrison), “The Land of Regrets”, in Damaris: A Novel, London: Hutchinson & Co. […], →OCLC, page 175:No, my dear boy, make yourself easy. They dare not lay a finger on me. As far as local unrest is concerned, there is no fear but that I shall be spared to die stupidly, rottingly, of old age in my bed.
2005, Jonathan DiMarco, Good Bullets Make Bad Neighbors: A Novel of Accidental Discharge, Narberth, Pa.: Zaltys Press, →ISBN, page 29:Then he took a fearless swig of the starchy latte. Pudding-like and rottingly sweet, it left a sticky milk moustache under his nose.