n. 1. Fitness; suitableness; appropriateness; as, the aptness of things to their end. [ 1913 Webster ]

The aptness of his quotations. J. R. Green. [ 1913 Webster ]

2. Disposition of the mind; propensity; as, the aptness of men to follow example. [ 1913 Webster ]

3. Quickness of apprehension; readiness in learning; docility; as, an aptness to learn is more observable in some children than in others. [ 1913 Webster ]

4. Proneness; tendency; as, the aptness of iron to rust. [ 1913 Webster ]