The word 'sojourn' entered Middle English around 1250 from Old French 'sojorner' (also 'sejorner'), meaning to stay temporarily, to dwell for a time. The Old French verb derives from Vulgar Latin *subdiurnāre, a compound of 'sub-' (under, during) and 'diurnum' (pertaining to the day), from Latin 'diēs' (day). At its etymological core, to sojourn is to spend a day — a meaning that expanded over centuries to cover any temporary residence, whether lasting hours or years.
The Latin root 'diēs' (day) traces back to PIE *dyew-, one of the most important roots in the Indo-European family. This root originally referred to the bright sky, the daylight, and the sky-god: Sanskrit 'Dyaus' (the sky god), Greek 'Zeus' (chief of the gods), Latin 'Iuppiter' (Jupiter, from *Dyeu-pater, 'sky father'), and Latin 'diēs' (day) all spring from this single source. The connection between the divine, the sky, and the daylight is primordial — in Proto-Indo-European culture, the bright daytime sky was itself a deity.
The semantic development from 'day' to 'temporary stay' passed through Vulgar Latin, the spoken Latin of the late Roman Empire that evolved into the Romance languages. *Subdiurnāre literally meant to pass the day somewhere, to stay under the day's duration. The prefix 'sub-' here functions in its temporal sense (during, for the duration of) rather than its spatial sense (under, below). This temporal use of 'sub-' also appears in Latin 'subito' (suddenly, literally 'under the moment').
Old French developed two important derivatives from *subdiurnāre: 'sojorner' (to stay temporarily) and 'sojorn/sejorn' (the noun, a temporary stay). Both crossed into English during the massive influx of French vocabulary following the Norman Conquest of 1066. By the mid-thirteenth century, English writers were using both the verb and noun forms.
The etymological kinship between 'sojourn' and 'journey' is one of the most elegant connections in English. 'Journey' comes from Old French 'journée' (a day's work, a day's travel), from Vulgar Latin 'diurnāta,' also derived from 'diurnum.' A journey was originally a single day's travel — the distance one could cover between sunrise and sunset. A sojourn was a single day's stay. Both words have since expanded well beyond their one-day
The word 'sojourn' has long carried literary and slightly formal connotations. In the King James Bible (1611), the word appears frequently: Abraham sojourns in Egypt, the Israelites sojourn in the wilderness. In biblical usage, 'sojourn' implies dwelling as a stranger or alien in a land that is not one's own — a temporary residence with the constant awareness that one does not fully belong. This theological resonance gives the word a depth that 'stay' or 'visit' cannot match.
Other members of the 'diēs' family in English include 'journal' (originally a daily record, from Old French 'jornal'), 'diary' (from Latin 'diārium,' a daily allowance, then a daily record), 'diurnal' (of or relating to the day), and 'adjourn' (from Old French 'ajorner,' to set a day for — originally meaning to summon to appear on a certain day, later to postpone to another day). The legal term 'adjourn' preserves the Latin 'day' more transparently: to adjourn a session is literally to assign it to another day.
In modern usage, 'sojourn' retains a literary or elevated register. One sojourns in a foreign city; one does not sojourn at a gas station. The word implies a stay of some duration, with a consciousness of its temporary nature, and often with connotations of cultural immersion or personal significance. NASA named one of its Mars rovers 'Sojourner' — a fitting name for a temporary visitor to an alien landscape, carrying with it the biblical resonance of dwelling as a stranger in a strange land.