Plural of diaeresis; marks or methods used in grammar and phonetics to show how syllables or sounds should be separated or pronounced.
From Greek diairesis (separation), from diairein (to divide), from dia- (apart) + hairein (to take). Originally a rhetorical term, evolved to mean various types of separation marks.
The diaeresis (that weird double-dot thing you see over vowels like in 'naïve') is basically a linguistic traffic cop telling you 'hey, don't blend these two vowels together!'
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