The compound adjective "twelfth-century" is a modern English formation that precisely dates a historical period by combining an ordinal number with a standardized time unit. The first element, "twelfth," originates from the Proto-Germanic twalif, meaning "two left over" (after ten), which evolved into the Old English ordinal twelfta. The second element, "century," derives from Latin centuria, a military and political division of one hundred, itself from centum, the Proto-Indo-European root for "hundred." The logical construction is purely chronological, fusing the concept of the 12th sequential period of one hundred years since a conventional starting point (often the birth of Christ) to denote the era from 1101 to 1200 AD.

Structure: twelfth + century twelfth: From Old English twelfta, related to twelf (twelve). The suffix -th forms ordinal numbers. Functional role: Specifies the ordinal position (12th). century: From Latin centuria, from centum (hundred). Functional role: Denotes a period of one hundred years.