deadline /ˈdɛdˌlaɪn/noun 4verb 1forms 3 noun4 •A time limit in the form of a date on or before which something must be completed.I must make this deadline or my boss will kill me! •(no longer used) A guideline marked on a plate for a printing press. •(no longer used) A line that does not move. •(no longer used) A boundary around a prison, prisoners crossing which would be shot. verb1 •To render an item non-mission-capable; to ground an aircraft, etc. formsdeadlined · deadlining · deadlines