What does it mean to "know" a word? I have heard/read most of the male words hundreds of times, and probably used them myself, but asked to define them I would be either inaccurate or unconfident. For example, I know that ailerons are flaps on an airplane, but I'm not sure which ones. I know that a femtosecond is a small unit of time, but I'm not sure what fraction of a second.
I find that giving a precise "dictionary definition" of a word is actually quite hard in general for many common words.
Anyway, the data is based on [1], which asks "I know this word"/"I don't know this word". It's also available in Dutch[2] which is a bit different and asks "this word exists"/"this word doesn't exist". Both tests include both actual words as well as made-up words. I did this test a few years back and my "score" was about 80% for Dutch (my native language) and 60% for English. I was a little but surprised by the fairly large gap between Dutch and English, since I've been speaking English almost exclusively for the last ten years (on account of living abroad), which goes to show just how hard it is to really learn a language to native-levels.
