propensity

(noun) an inclination to do something. Synonyms: leaning, tendency. Example: "He felt leanings toward frivolity."

(noun) a natural inclination. Synonyms: proclivity, leaning. Example: "He has a proclivity for exaggeration."

(noun) a disposition to behave in a certain way. Synonyms: aptness. Examples: "The aptness of iron to rust." "The propensity of disease to spread."