My assessor is giving me spelling advice - but he's wrong I'm writing the thesis on which I aim to graduate with a bachelor's degree. I've got an incredibly nice assessor, whom I sent part of it, and he gave a lot of helpful feedback on structure, relevant and irrelevant details, et cetera.

But he also suggested that a word is spelled wrong, when it isn't. Now, this isn't just any word; it is the name of the product I am creating as an IT student. Not the proper name, because that would be exempt from spelling conventions, but the generic name with which I refer to it very often; like, several hundred times, scattered over not just my thesis but all the relevant documentation.

This isn't a question about the spelling itself - the word is in Dutch anyway. But I want to know if I should be adopting his wrong advice because it comes from the person who is going to grade me; or engage in spelling debate which can come across as pretentious. It doesn't help that I'm a language nerd and that this isn't something to be settled with a single link to a dictionary; the term itself is a new compound, and there are specific rules for forming those that I consciously followed.
First of all: ask for a third opinion, just to be sure you are right.

Anyway, the nice thing about science people is that they are usually convinced by evidence, even when it goes against their previous thoughts. Write them a polite, respectful e-mail explaining why you think you are right, and pointing out reputable grammar sources to back you up. Show that you have done some additional research. There are good chances that this will work.