The word "Sunday" is a direct calque, or loan translation, from the Latin phrase diēs Sōlis, meaning "day of the Sun". This Latin name was itself a translation of the ancient Greek hēméra Hēlíou. The naming convention reflects the ancient Hellenistic practice of dedicating each day to one of the seven classical planets, which included the Sun. In Old English, the Latin term was directly rendered as Sunnandæg, literally "Sun's day", a compound of sunne (sun) and dæg (day), which has evolved into the modern "Sunday". This etymology preserves the literal meaning of the day dedicated to the solar body, a concept inherited from pre-Christian astronomical and calendrical systems.

Structure: sun (the sun) + day (a 24-hour period) - sun: From Old English sunne, meaning "the sun". Its ultimate origin is Proto-Germanic sunnōn and Proto-Indo-European sóh₂wl̥, meaning "the sun". - day: From Old English dæg, meaning "day, a 24-hour period". Its ultimate origin is Proto-Germanic dagaz and Proto-Indo-European dʰegʷʰ-, meaning "to burn, be hot".