tendency vs propensity

tendency and propensity both are nouns.

Word	Noun	Adjective	Verb	Adverb
tendency	Yes	No	No	No
propensity	Yes	No	No	No

As nouns, propensity is a hyponym of tendency; that is, propensity is a word with a more specific, narrower meaning than tendency:

tendency: an attitude of mind especially one that favors one alternative over others
propensity: a natural inclination

As nouns, tendency and propensity are synonyms defined as:

Other synonyms of tendency include leaning.

tendency (noun)	propensity (noun)
a characteristic likelihood of or natural disposition toward a certain condition or character or effect	a disposition to behave in a certain way
an attitude of mind especially one that favors one alternative over others	a natural inclination
an inclination to do something	an inclination to do something
a general direction in which something tends to move