Plural of frenum, which is a small band of tissue that connects or restrains something, commonly found under the tongue.
From Latin frena, plural of frenum meaning 'a bridle or rein.' The term refers to structures that physically restrain or limit movement, just as a bridle restrains a horse.
Your tongue's little connector strip has the same root word as 'bridle'—that's because both limit movement, so doctors borrowed the horse-control vocabulary to describe what your body does internally!
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