Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Perseus.
cŏoptātĭo, ōnis, f. [co-opto], an election, choice: collegiorum, Cic. Lael. 25, 96: censoria, id. Leg. 3, 12, 27: in Patres, i. e. a confirmation by the Senate of Senators nominated by the king, Liv. 4, 4, 7 Weissenb. ad loc.; Flor. 4, 4.