sensitiveness vs sentiency

sensitiveness and sentiency both are nouns.

Word	Noun	Adjective	Verb	Adverb
sensitiveness	Yes	No	No	No
sentiency	Yes	No	No	No

As nouns, sentiency is a hypernym of sensitiveness; that is, sentiency is a word with a broader meaning than sensitiveness:

sensitiveness: (physiology) responsiveness to external stimuli; the faculty of sensation
sentiency: the faculty through which the external world is apprehended

Other hypernyms of sensitiveness include sensation, sense, sensory faculty, sentience.

sensitiveness (noun)	sentiency (noun)
the ability to respond to physical stimuli or to register small physical amounts or differences	the faculty through which the external world is apprehended
the ability to respond to affective changes in your interpersonal environment
(physiology) responsiveness to external stimuli; the faculty of sensation
sensitivity to emotional feelings (of self and others)