Dictionaries aren't very consistent, are they? In the online version they are as follows:
antonyms: incompetent, inept, poor, unfit, unfitted, unqualified
related words: accomplished, ace, adept, experienced, expert, master, masterful, masterly, practiced, proficient, seasoned, skilled, skillful, veteran, overqualified, prepared, schooled, trained, apt, ready, willing, all-round, protean, versatile.
In the online Webster dictionary definition, able means: to have a particular physical or mental skill.