Used in the sense of no or none, to show lack of or failure to perform; or in the sense of not, to negate the meaning of the word to which it is prefixed.
prevocalic form of nona-
under-
prefix
Deficient, below what is correct
Behind
Beneath, under
Subordinate to
How often have the words non- and under- occurred in a corpus of books? (source: Google Ngram Viewer )