An excuse used to avoid responsibility or a failure to do something one is expected or obligated to do.
From co- plus out, or possibly from 'co-operate out.' The term emerged in American slang in the mid-20th century, gaining prominence in the 1960s counterculture as a critical term for avoiding social obligations.
The etymology is slightly mysterious—some linguists think it comes from 'cop' (to steal/take) plus 'out,' while others argue it's just 'co-' plus 'out' meaning 'back away'—the slang origin makes its exact roots hard to trace.
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