dieresis vs diaeresis

dieresis and diaeresis both are nouns.

Word	Noun	Adjective	Verb	Adverb
dieresis	Yes	No	No	No
diaeresis	Yes	No	No	No

As nouns, dieresis and diaeresis are synonyms defined as:

dieresis and diaeresis: a diacritical mark (two dots) placed over a vowel to indicate that it does not form a diphthong with an adjacent vowel

dieresis (noun)	diaeresis (noun)
a diacritical mark (two dots) placed over a vowel to indicate that it does not form a diphthong with an adjacent vowel	a diacritical mark (two dots) placed over a vowel to indicate that it does not form a diphthong with an adjacent vowel