The extreme limits of settled land or knowledge; unexplored or undeveloped regions or areas of study.
From Old French 'frontiere' meaning boundary, derived from Latin 'frons' (forehead, front). Originally referred to military boundaries between territories, later expanded to mean any edge of civilization or knowledge.
The word 'frontier' originally meant the part of an army facing the enemy, literally the 'forehead' of military formation. Today's Silicon Valley tech companies cleverly use this military metaphor when they talk about 'pushing the frontiers' of innovation.
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