Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
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.