How about something as simple as "giant." With the slurring of words it make sense, especially if If Thomas didn't know what it was he might have gone with a simple description. In that case it could be anything that's really big.
Personally, I don't trust Justine. She was way more capable in the short story Even Hand than we've ever seen her in the books and there's never been a reasonable explanation how she became steady minded. In Grave Peril, Justine revealed that being with Thomas barely kept her sane, but somehow after almost being killed by Thomas she made a more than full recovery and eventually became the Raith office manager and after that a double agent working for both Lara and Harry. As Harry's spy she just collects information, but we know from Even Hand that she has done field work for Lara, and done it well. It's like Jim expects us to ignore Justine because Harry sees her as both incredibly sexy but also very sweet and; not innocent exactly, but something nice and maybe just a little too good to be true.
Giant seems more likely than Jotun. But "Gi" sounds different from "Ju". "Jn" is closer.
As for suspecting Justine, Cold Days left me with the impression that Nemesis/Maeve was interested in her but not that she was already infected. Unless she was, and somehow suppressed it, and they were curious.
I think the Thomas + Justine True Love goes a fair way to defending her character, particularly from the angle of being loyal to Thomas.
That said, I've yet to see a theory that resolves the "why exactly did Thomas attack Etri?" question satisfactorily.
1) He wasn't, he was trying to warn him and got interrupted and blamed by the bad guy.
2) He was enthralled by someone and only snapped out of it after the mission.
Either one would probably revolve around Evanna, with him visiting her after the Eb talk to feed, and either being enthralled by her or an ally, or him happening across info or overhearing a conversation and decided to get to Etri by setting the explosives to distract the guards.
