Sayadaw is the Burmese title for a senior and respected monk, originally meaning royal teacher and given to the abbots who tutored kings.
From royal tutor to senior monk
The word originally denoted the eminent monks who served as teachers to the Burmese kings, and it broadened into the general title for a senior and venerable monk, above all the abbot of a monastery, so the term now marks seniority, learning and the office of abbot rather than a specifically royal connection. The sayadaw is the head of a monastic community and a teacher of the monks and the laity, and the most eminent bear the title as one of high honour.
Teachers of the tradition
Burma has produced a line of renowned sayadaws whose scholarship and meditation teaching have been of great influence, including masters who shaped the modern revival and worldwide spread of insight meditation, so the title is associated with some of the most consequential Buddhist teachers of the modern era. Entry to the standing is by seniority, learning and the holding of monastic office, and the honorific rests on those rather than on any formal conferral. The sayadaw thus corresponds in Burmese Buddhism to the senior teaching monk and abbot, the counterpart of the ajahn of Thailand, and the title marks the venerable elder of the monastic community, the teacher whose standing has grown with his years, his learning and his responsibility for the formation of others in the path.