Leaning, propensity, proclivity, penchant, flair mean a strong instinct or liking for something or sometimes someone.
One has a leaning toward something (as a church, a party, or a school of philosophy) when one definitely inclines to attachment to it or to follow it as a pursuit, a profession, or a course of action. Leaning, however, indicates only the direction in which one is being drawn by the force of attraction; it carries no implication of one's final course or destination.
One has a propensity (as toward or for something or to do something) when one has an innate or inherent and often uncontrollable longing or is driven by a natural appetite.
One has a proclivity (as for or towards something or to do something) when one is prone to something not only by natural inclination but also by habitual indulgence or by the peculiarities of one's constitution or temperament.
Proclivity often implies a tendency toward evil; when it is used without this implication, it still implies a stronger and less controllable urge than the other words here considered.
One has a penchant usually for something when it has an irresistible attraction for him or when he has a decided taste for it.
One has a flair for something when one has such an instinct for it as leads one to it as if by the very nature of one's being. Often, especially in extended use, flair implies acumen and an innate power of discernment that results in an ability to distinguish the genuine from the counterfeit, the valuable from the valueless, and the significant from the insignificant.
Sometimes, the notion of "to do" is substituted for that of "to distinguish" and flair becomes a close synonym of knack, aptitude, or talent.