Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
prĕhensĭo or prensĭo, ōnis, f. [prehendo], a seizing, apprenending.
Lit. (ante-class.): tribuni plebis prensionem habent, the right of arresting any one, Atei. Cap. ap. Gell. 13, 12, 4: in magistratu habent alii vocationem, alii prensionem, Varr. ib. (in Caes. B. C. 2, 9, 6, the true reading is pressionibus).