Lewis & Short

crēbresco (in MSS. and edd. sometimes euphon. crēbesco, bŭi, like rubesco, from ruber), brŭi, 3, v. inch. [creber], to become frequent, to increase, grow strong; of a rumor, report, to spread abroad (perh. not ante-Aug.; most freq. in Tac.): crebrescunt optatae aurae, Verg. A. 3, 530: gestus cum ipsā orationis celeritate, Quint. 11, 3, 111: horror, Verg. A. 12, 407: bellum, Tac. H. 2, 67: tum crebescere fragor, Plin. Ep. 7, 27, 8: seditio, Tac. H. 1, 39: licentia et impunitas, id. A. 3, 60: invidia, id. H. 3, 34: sermo, Verg. A. 12, 222; so, fama cladis Germanicae, Tac. H. 4, 12.
With a clause as subject: per socios crebrescit vivere Agrippam, etc., is noised abroad Tac. A. 2, 39.
Rare in perf. and pluperf.: jamque rumor publice crebuerat, App. M. 10, p. 247: tam multa bella ubique crebuerunt, Aug. Civ. Dei, 3, 17.