schwa

In linguistics, specifically phonetics and phonology, schwa can mean:An unstressed and toneless neutral vowel sound in any language, often but not necessarily a mid-central vowel. Such vowels are often transcribed with the symbol <>, regardless of their actual phonetic value.The mid-central vowel sound (rounded or unrounded) in the middle of the vowel chart, stressed or unstressed. In IPA phonetic transcription, it is written as <>. In this case the term mid-central vowel may be used instead of schwa to avoid ambiguity.The Latin letter ə and the Cyrillic letter ә (see the respective articles).
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n. (Hebrew) schwa, unstressed vowel sound (represented phonetically by a backwards and upside-down "e")

Noun
1. a neutral middle vowel; occurs in unstressed syllables
(synonym) shwa
(hypernym) vowel, vowel sound
(hyponym) murmur vowel, murmur

The inverted e used to symbolized a relaxed vowel sound which is neither short nor long