a speech sound made with the vocal tract open
"The teacher explained that sounds like 'a' and 'o' are vowels because they are produced with an open vocal tract, unlike consonants which involve some blockage."
a letter of the alphabet standing for a spoken vowel
"When learning to read, children often get confused between consonants and vowels because they are letters that represent actual speech sounds."
A sound produced by the vocal cords with relatively little restriction of the oral cavity, forming the prominent sound of a syllable.
"The teacher asked the students to hum their vowels without moving their lips or teeth too much."
To add vowel points to a consonantal script (e.g. niqqud in Hebrew or harakat in Arabic)
"The scribe carefully voweled the ancient manuscript so that readers would know exactly where to place their breaths between the unmarked letters."
The word "vowel" comes from the Old French vouel and the Latin vōcālis, which means "voiced." It originally referred to a sound produced with voice, rather than just a letter in an alphabet.