Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. dēlapsus, a, um, Part. from delabor.
* 2. dēlapsus, ūs, m. [delabor], a falling off, descent: aquae, a flowing off, discharge, Varr. R. R. 1, 6 fin.