To make something illegitimate, impure, inferior, or corrupted; to debase or adulterate something (American spelling).
From bastard + -ize (American suffix from Greek -izein). The verb extends bastard from a noun describing a person to an action verb describing corruption of things.
This verb became incredibly popular in 19th-century literary criticism when writers worried about language and culture being 'bastardized' by foreign influences—it reveals anxieties about national purity.
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