To refrain from speaking, especially when you want to say something critical or inappropriate; to hold back your words.
This phrase dates to the 16th century and references the literal act of biting one's tongue to prevent speech. The physical pain of tongue-biting serves as a metaphor for the difficulty and discomfort of suppressing one's immediate verbal reactions.
The phrase captures the genuine physical tension we feel when restraining speech - our tongue literally wants to move to form words, and stopping it requires muscular effort. Neuroscience confirms that suppressing speech activates the same brain regions involved in physical self-control, making this metaphor remarkably accurate.
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