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The best meaning for dereliction is to neglect or be negligent, careless.
Dereliction of duty means failing to do the task you were charged with. Eg. Falling asleep whilst guarding something.
derelictions
"Patent" in this case means obvious or apparent. If you show patent dereliction of duty, you are obviously not doing your job.
The escaped convict was found by the police in the nearbyderelict house.