Our study offers a thorough analysis of a specific adverb in a prose of one author. It fills a gap on the adverbs’s researches in Latin prose in general and in the Tacitean corpora in particular by examining the unique usages of crēbrō/crēbrius/crēberrimē in his treatises. Our grammatical approach is descriptive and enables us to present the full documentation of the adverb in the selected corpora. Our main results are: crēbrō/crēbrius/crēberrimē is documented mainly in Ann., rarely in Hist. and Ag. It occurs in positive crēbrō, comparative crēbrius and seldom in superlative crēberrimē denoting a lengthy and non-continuous time with the meaning “often/frequently”, “more/most often/frequently”. The adverb refers to the past and seldom to the present or future. Only the comparative adverb crēbrius is followed by quam with a contrast concerning content. The adverb is rarely in proximity to a contemporaneous adverb with saepe or posterior adverb with simul. The modified parts of speech are usually finite verbs in the past tenses in perfect, imperfect and pluperfect, seldom participia, infinitives or an elliptic verb. Crēbrō/crēbrius/crēberrimē is placed only before the modified part of speech, mostly in first position before it, and sometimes in third position and further removed before it. Crēbrō as compared with crēbrius and crēberrimē yielded identical and different features. Keywords: adverb, comparison, contemporaneous, explicit, finite verb, crēbrō/crēbrius/crēberrimē, multiple clause, parallel, posterior, syntactic position