month-long

The compound adjective "month-long" is a transparent formation from two native English elements. "Month" originates from the Proto-Germanic mēnōþs, itself derived from the Proto-Indo-European root mē- meaning "to measure," reflecting the moon's role as an ancient time-measurer. "Long" stems from the Proto-Germanic langaz, tracing back to the Proto-Indo-European root dlongʰos-, meaning "long." The compound logically combines these concepts, where "month" specifies the measured unit of time and "long" describes the extent, directly yielding the modern meaning of an event or state persisting for the duration of a calendar month.

Structure: month (time period) + long (duration) - month: From Old English mōnaþ, related to mōna (moon), indicating a unit of time based on the lunar cycle. Its functional role is the noun base specifying the unit of measurement. - long: From Old English lang, long, meaning "having considerable linear extent in space or duration in time." Its functional role is the adjective describing the extent of the duration.