Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dē-cōlo, āvi (old fut. perf. decolassit = decolaverit, Plaut. Cas. 2, 4, 28), 1, v. n. [colum; lit., to trickle from or through; hence trop.], to come to naught, to fail (ante-class.): si spes decolabit, Plaut. Gapt. 3, 1, 37; cf. id. Casin. 2, 4, 28: quorum si alterutrum decolat, Varr. R. R. 1, 28.