It appears to be a very obscure technical term from linguistics. Only nine google hits in total. I've never seen or heard in my first 66 years, and I don't expect to ever see or hear it again. So in my opinion, neither you nor I need to worry about its meaning.
I think some of those hits might include typos. Some results I've checked had 'naminalization' in the preview where all the hits are listed but when I followed through, the word in the actual text was 'nominalization'.