Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
invŏcātĭo, ōnis, f. [invoco], an invoking, invocation (post-Aug.): deorum, Quint. 6, 1, 33: dearum, id. 6, 1, 48.
Absol., Quint. 9, 2, 104; 11, 3, 115; Macr. S. 1, 16.