Consonant
A consonant was a specific sound made in verbal communication, as opposed to a vowel.

The Preservers' obelisk on Amerind could be opened either by playing certain musical notes or by speaking a series of vowels and consonants in their proper sequence. ()

A reversal of consonant and vowel was metathesis, which made Captain Picard call a  crewmember Mister "" instead of "Barclay". ()

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Linguistics