Definition - The lengthening of a syllable or a vowel.

Example -
It was soooo big!

Etymology -
The word derives from the Greek dia, asunder + stellein, to place.

Oxford English Dictionary -
Its first citation is from 1580:
"Heaven being used shorte as one sillable, when it is in verse stretched out with a Diastole, is like a lame dogge that holdes up one legge."
(Spenser To Master G.H. Wks. (Globe) App. ii. 709/1)

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