The compound adjective "week-long" is a transparent formation from two ancient Germanic roots. "Week" originates from the Proto-Germanic wikōn, likely related to a notion of change or succession, which evolved into the standard unit of seven days. "Long" descends from the Proto-Germanic langaz, meaning "having great linear extent or duration." The compound logic is straightforwardly literal, combining the specific time unit with the adjective denoting extended duration. This pattern of "[time unit]-long" is productive in English, creating clear and efficient adjectives like "day-long," "month-long," and "year-long" to describe events or states persisting for the entirety of that period.

Structure: week (period of seven days) + long (having great duration) - week: From Old English wice, wicu, of Germanic origin. Functions as the base noun specifying the unit of time. - long: From Old English lang, long, of Germanic origin. Functions as an adjective describing the extent or duration.