The precise etymology of the modern anglicised word "Assam" is ambiguous. In the classical period and up to the 12th century the region east of the Karatoya river, largely congruent to present-day Assam, was called Kamarupa, and alternatively, Pragjyotisha. In medieval times the Mughals used Asham (eastern Assam) and Kamrup (western Assam), and during British colonialism, the English used Assam. Though many authors have associated the name with the 13th century Shan invaders the precise origin of the name is not clear. It was suggested by some that the Sanskrit word Asama ("unequalled", "peerless", etc.) was the root, which has been rejected by Kakati, and more recent authors have concurred that it is a latter-day Sanskritization of a native name. Among possible origins are Tai (A-Cham) and Bodo (Ha-Sam).