synesthesia vs synaesthesia

synesthesia and synaesthesia both are nouns.

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

As nouns, synesthesia and synaesthesia are synonyms defined as:

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

synesthesia (noun)	synaesthesia (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