Referred to as such in episode dialogue, or in material not presented on-screen?
After spending 10 minutes utilizing my web browsers find function on Chrissie's transcript site (http://www.chakoteya.net/
), I can confirm that the term "Secondary Hull" is not spoken on-screen in any of the original, animated or first 6 TOS movies
Yeah, that's the same result I was coming up with. "Secondary hull" appears in dialogue once in TNG, but doesn't seem to have become a regular part of the jargon until Voyager, where it turns up quite a few times. I think that portion of the ship was mostly referred to as the "Engineering section" in TOS (also in several TNG eps.)
Speaking of Chrissie's/Chakoteya's site for a moment: has anyone had trouble accessing that site lately - say, over the last three months or so? Other than the odd temporary downtime, I've been using the site for years without issue, but since February or early March, my browser has crashed immediately every time I click on a link or bookmark to go there. Kinda frustrating, as it's been a very useful resource.