nincompoop

Uncertain; the first element nincom- is possibly from the name Nicholas or Nicodemus (compare French nicodème (“foolish or gullible person”), from the Pharisee named Nicodemus mentioned in the Bible who asks Jesus seemingly naive questions: see John 3:1–21), or from ninny (“foolish or silly person”), while the second element -poop could be derived from poop (“(obsolete) to cheat, deceive, fool”). The English lexicographer Samuel Johnson (1709–1784) suggested that the first element might be from Latin non compos (mentis) (“not of sound mind”), but the Oxford English Dictionary notes that this does not correspond with early forms of the word from the 16th century such as nickumpoop and nicompoop.