synaesthesia vs aesthesis

synaesthesia and aesthesis both are nouns.

Word	Noun	Adjective	Verb	Adverb
synaesthesia	Yes	No	No	No
aesthesis	Yes	No	No	No

As nouns, aesthesis is a hypernym of synaesthesia; that is, aesthesis is a word with a broader meaning than synaesthesia:

synaesthesia: a sensation that normally occurs in one sense modality occurs when another modality is stimulated
aesthesis: an unelaborated elementary awareness of stimulation

Other hypernyms of synaesthesia include esthesis, sensation, sense datum, sense experience, sense impression.

synaesthesia (noun)	aesthesis (noun)
a sensation that normally occurs in one sense modality occurs when another modality is stimulated	an unelaborated elementary awareness of stimulation