Lewis & Short

com-murmŭro, āre, 1, v. n., or com-murmŭror, āri, 1, v. dep., to murmur to one’s self or with others (very rare).

  1. I. Act. form: clauso commurmurat ore, Sil. 15, 821: (ciconiae) congregatae inter se commurmurant, Plin. 10, 23, 31, § 62.
  2. II. Dep. form: ut scriba secum ipse commurmuratus sit, Cic. Pis. 25, 61: commurmurantur αὐτοί, Varr. ap. Non. p. 178, 9 (Sat. Men. 64, 8).