Lewis & Short

dē-clāmo, āvi, ātum, 1, v. n. and a.
Rhetor. t. t., to exercise one’s self in rhetorical delivery, to practise speaking, to declaim. For syn. cf.: dictito, concionor, pronuntio, palam dico, praedico, recito, declamito. (Class., most freq. in Cic. and Quint.)

  1. I. In a good sense.
          1. (α) Neutr.: ad fluctum aiunt declamare solitum Demosthenem, ut fremitum assuesceret voce vincere, Cic. Fin. 5, 2, 5; id. fragm. ap. Quint. 6, 3, 73: dum tu declamas Romae, * Hor. Ep. 1, 2, 2: declamare doces? Juv. 7, 150: haec est sedes orationis, hic laus omnis declamantium, Quint. 9, 4, 62 (al. declamat) et saep.
            Pass. impers.: in eo, quomodo declametur, positum est etiam, quomodo agatur, Quint. 9, 2, 81.
          2. (β) Act. (rare; not in Cic.; cf., on the contrary, declamito, no. I. β): suasorias, Quint. 3, 8, 61.
    1. B. Poet., in gen., to speak oratorically, to declaim: quis nisi mentis inops tenerae declamet amicae? Ov. A. A. 1, 465.
  2. II. In a bad sense, to speak as an orator with violence, to declaim, to bluster, bawl: ille insanus, qui pro isto vehementissime contra me declamasset, Cic. Verr. 2, 4, 66 fin.; so in quemvis, id. Fam. 3, 11, 2: aliquid ex alia oratione declamare, id. Rosc. Am. 29 fin.