Most capable; the superlative form indicating the greatest degree of ability or competence.
From capable plus -est, the standard English superlative suffix. Like capabler, it represents older synthetic superlatives that modern English often replaces with 'most capable.'
'Capablest' sounds archaic today because English has shifted toward analytic forms—but in Shakespeare's time, people said 'capablest' all the time, and that -est ending was the normal way to form superlatives.
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