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"Endurance" yields: ability, allowance, backbone, bearing, capacity, continuing, cool, coolness, courage, enduring, forebearance, fortitude, grit, guts, gutsiness, heart*, holding up, intestinal fortitude, mettle, moxie*, patience, perseverance, persistence, pertinacity, pluck, resignation, resistance, resolution, restraint, spunk, stamina, standing, starch*, strength, submission, sufferance, suffering, tenacity, tolerance, toleration, undergoing, vitality, will, withstanding
"Perseverance" yields: backbone*, constancy, continuance, cool, dedication, determination, doggedness, drive, endurance, grit*, guts*, immovability, indefatigability, moxie*, persistence, pertinacity, pluck*, prolonging, purposefulness, pursuance, resolution, sedulity, spunk, stamina, steadfastness, stick-to-itiveness, tenacity
"Mettle" yields: animation, ardor, backbone, bravery, caliber, courage, daring, dauntlessness, disposition, energy, fire, force, fortitude, gallantry, gameness, grit*, guts*, hardihood, heart*, indomitability, kidney, life*, makeup, moxie, nature, nerve, pluck, quality, resolution, resolve, spirit, spunk, stamina, stamp*, starch, temper, temperament, valor, vigor, vitality