synaesthesia vs synesthesia

synaesthesia and synesthesia both are nouns.

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

As nouns, synaesthesia and synesthesia are synonyms defined as:

synaesthesia and synesthesia: a sensation that normally occurs in one sense modality occurs when another modality is stimulated

synaesthesia (noun)	synesthesia (noun)
a sensation that normally occurs in one sense modality occurs when another modality is stimulated	a sensation that normally occurs in one sense modality occurs when another modality is stimulated