Making something more tight, snug, or firm, or becoming more restrictive or difficult.
From 'tight,' which comes from Old English and Germanic roots meaning 'dense' or 'firmly packed.' The verb form with '-en' suffix emerged in Middle English to describe the action of making something tight.
The metaphorical use of 'tightening' is fascinating—we say a 'tight economy' or 'tightening security' to describe control and restriction, borrowing the physical sensation of something gripping you to describe abstract social pressures.
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