aptness

Etymology

apt + -ness

noun

1. suitability; the quality of being apt or suitable
   A regular supply of coking slack is sent from Durham to the Scunthorpe area, in view of its special aptness for steelmaking processes, …. 1962 August, G. Freeman Allen, “Traffic control on the Great Northern Line”, in Modern Railways, page 128
2. disposition of the mind; propensity
   the aptness of men to follow example
3. speed or readiness in learning; docility
   An aptness to learn is more observable in some children than in others.
4. proneness; tendency
   the aptness of iron to rust