Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
fistūco, no perf., ātum, 1, v. a. [fistuca], to ram down or in, to ram fast: fundamenta, Cato, R. R. 18, 7: solum, Plin. 36, 25, 63, § 188; Vitr. 7, 4 fin.: rudus pedali crassitudine, Plin. 36, 25, 62, § 186.
In the part. perf. absol.: terram circa radices fistucato spissandam, by ramming down, i. q. fistucatione, Plin. 17, 11, 16, § 87.