marplot UK /ˈmɑːplɒt/US /ˈmɑɹplɑt/adjective 1noun 1forms 3 adjective1 •(no longer used) Ruining a plan, interfering, spoilsport.Let us argue the point with this pert, unruly, marplot conscience of mine… — 1792 noun1 •Synonym of spoilsport, one who ruins other's plans or enjoyment of something.“The old marplot has discovered the baby,” Monica whispered. “I suppose it cried and woke him up, and now he thinks he's witness to a miracle.” — 1920 formsmarplots · more marplot · most marplot