1. Fitness; suitableness; as, the aptness of things to their end.
2. Disposition of the mind; propensity; as, the aptness of men to follow example.
3. Quickness of apprehension; readiness in learning; docility; as, an aptness to learn is more observable in some children than in others.
4. Tendency, in things; as, the aptness of iron to rust.