The behavior, practices, or character traits of a blackguard; unprincipled, dishonorable, or scoundrelish conduct.
From 'blackguard' (a dishonest or disreputable person) plus '-ism' (a system or practice), forming an abstract noun describing the philosophy or pattern of such behavior.
'Blackguard' originally referred to kitchen servants with black uniforms in medieval courts, but shifted to mean 'rogue' or 'scoundrel'—showing how a descriptive job title became an insult.
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