This is a long, funny-sounding word for a silly person. A silly word, you might say, a word that sounds like what it means!
We might know what it means, but do we know where it comes from? The short, most honest answer is no, we don’t. Not for sure. However, there are a few ideas that have been put forward as to its origin.
Back in 1755, when Dr Johnson was writing his Dictionary, he suggested that the word was from a Latin phrase; non compos mentis, with the first two words, non compos, forming the word we know today. This might seem like a logical assumption, given that non compos mentis means “not of sound mind”.
Some of the objections put forward against this theory is that it fails to take into account other versions of the word. The Oxford English Dictionary gives the earlier examples nicompoop and nickumpoop, while scholars point out that the second “n” is missing from the beginning of the word in these early forms.
Personally, I don’t see these objections as major problems. It would hardly be the first time that a word had lost a consonant, or that alternative versions of a word with slightly differing consonants had arisen.
The Oxford English Dictionary puts forward a curious proposition; that nincompoop may derive from the name Nicholas or from Nicodemus. This latter was a Pharisee known for his questioning of Christ, who might perhaps have been seen as naïve or out of his depth. In this instance, we can compare with nicodème from French, which means “simpleton”.
This is indeed interesting, but if you object to Johnson’s etymology on the grounds of a missing n, or varying forms, I think it would be hard to make a case for such a major change as Nicodemus turning into nincompoop, especially without intermediate forms to back up your case. However, I should state that this theory appears to be gaining ground.
In short, all we have on this word are guesses, but no certainties. Which is perhaps apt, as that is sometimes all the insight we have into the minds of the people it is intended to describe. So where does that leave us?