What does aptitude mean?
The definition of aptitude
Apt”i*tude, n.
Etym: [F. aptitude, LL. aptitudo, fr. L. aptus. See Apt, and cf. Attitude.]

1 A natural or acquired disposition or capacity for a particular purpose, or tendency to a particular action or effect; as, oil has an aptitude to burn. He seems to have had a peculiar aptitude for the management of irregular troops. Macaulay.
2 A general fitness or suitableness; adaptation. That sociable and helpful aptitude which God implanted between man and woman. Milton.
3 Readiness in learning; docility; aptness. He was a boy of remarkable aptitude. Macaulay.