What is "quantitative metathesis"

n. (context prosody English) A form of metathesis or transposition involving quantity or vowel length, by which two neighboring vowels – one long, one short – switch their lengths, so that the long one becomes short, and the short one becomes long.

Quantitative metathesis (or transfer of quantity) is a specific form of metathesis or transposition (a sound change) involving quantity or vowel length. By this process, two vowels near each other – one long, one short – switch their lengths, so that the long one becomes short, and the short one becomes long.

In theory, the definition includes both

long-short → short-long

and

short-long → long-short,

but Ancient Greek, which the term was originally created to describe, displays only the former, since the process is part of long-vowel shortening.