People considered to be disreputable, undesirable, or of low social status; the common rabble or unruly crowds.
From Old French 'rif et raf' (plunder and scraps), combining 'rif' (riffle) and 'raf' (raff). The term became English in the 16th century as a derogatory term for common people or troublemakers.
Riffraff is a perfect example of 'class prejudice words'—it was specifically created by wealthy people to dismiss the lower classes! The reduplicated structure (rif-raf) mimics the sound of something tumbling or chaotic, making the insult even more dismissive.
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