Lewis & Short

collŏcūtĭo (conl-), ōnis, f. [colloquor], a (familiar or private) conversation, conference (very rare): hominum, Cic. Tusc. 1, 13, 30; id. Att. 12, 1, 2: venire cum aliquo in collocutionem, Auct. Her. 1, 15, 25.
In plur.: familiarissimae cum aliquo, Cic. Phil. 11, 2, 5: in sermonibus collocutionibusque aliquid videre, id. Fam. 1, 9, 4.