‘Day’ and ‘night’ in Latin

Although Latin is rich in vocabulary items for time, the history of their formation is not always clear. The adjectives and adverbs related to ‘day’ and ‘night’—diurnus ‘of the day’ / dius ‘by day’ and nocturnus ‘of the night’ / nox ‘by night’—are such cases and have not yet received fully satisfactory morphological explanations, particularly as to the -r- of the adjectives and the word-final sibilant of the adverbs, from either a Latin or an Indo-European perspective. Building upon traditional views, this paper offers a fresh approach to these forms. The results will then be applied to another temporal adjective, mēnstruus ‘of a month’, to clarify its phonological and morphological peculiarities.