Solemn promises or commitments to do something, or items given as security for a loan.
From Old French 'plege,' possibly from Germanic roots. The meaning shifted from 'hostage' or 'guarantee' to 'a promise,' connecting the idea of putting something up as security with making a commitment.
Pledges in fraternity culture became so common that 'pledge' shifted from formal oath to hazing, showing how words can change meaning when subcultures adopt them and apply them differently than the mainstream.
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