1Of good disposition, morals, or behaviour; having good qualities; right-minded. Now rare (chiefly archaic).
2In good physical condition; in a sound, healthy, or satisfactory state.
Such that a small error in measurement or change in data gives rise to only a small change in the calculated result or outcome; such that an answer can be obtained to an acceptable degree of accuracy.
Late Middle English; earliest use found in Edward, Duke of York (fl. c1373–1415), magnate. From well + conditioned.