Lewis & Short

sermōcĭnor, ātus, 1, v. dep. n. [sermo].

  1. I. To talk with any one, to parley, converse, commune, discourse about any thing (rare but class.; syn. colloquor): consuetudo sermocinandi, Cic. Inv. 2, 17, 54: cum aliquo, id. Verr. 2, 1, 52, § 138: psittaci etiam sermocinantes, Plin. 10, 41, 58, § 117.
    Act. collat. form sermōcĭno, Isid. Orig. 1, 39, 2.
  2. II. In partic. (acc. to sermo, I. B. 1.), to hold a literary conversation, to dispute, discuss: exquisitius sermocinari, etc., Suet. Tib. 56: pluria forte quis dixit sermocinans vir apprime doctus, Gell. 5, 21, 1.
    Hence, * sermōcĭnanter, adv., in discourse or conversation: horas extrahere, Sid. Ep. 8, 6 med.