This paper investigates the semantic-pragmatic functions of the Japanese adverb zenzen (全然) ‘completely, entirely, not at all’ highlighting its semantic and functional development from its initial borrowing from the Chinese etymon to its contemporary use. The goal of the study is to investigate how zenzen is used in spoken discourse and what functions it has from the perspective of cooptation, subjectification, and intersubjectification. The paper traces the historical trajectory of zenzen from the early Meiji Period to the present, analyzing quantitative data from six corpora. A total of 2,154 examples were analysed. The results showed that in contemporary Japanese, zenzen serves to accentuate a state of perfection and reassurance, reflecting the speaker’s attitude toward the interlocutor. The paper argues that zenzen has evolved as a pragmatic marker, indicating the speaker’s epistemic stance and viewpoint. The paper attempts to explain how zenzen has transitioned from a lexical item with objective meanings to a pragmatic marker with (inter)subjective functions. The findings of the paper indicate that, zenzen functions as an adjectival noun combined with copula -da/-desu ‘to be’, creating a new unique construction [ zenzen-da/desu ]. These constructions play a role in expressing (inter)subjective meanings. The findings of the paper will prove useful in expanding our understanding of how diachronic language changes occur from the perspectives of cooptation, subjectification, and intersubjectification.