What I mean by missable is, if you miss it the first time you go to the dungeon or location you cannot get it at latter time by revisiting it.
Only one, namely storm call, is missable, and that's when you visit sovngrade/heaven or something. Is there another one?
I just revisited Saarthal. I no longer have the amulet and I've heard people having trouble. Yet, I went through the dungeon just fine with no issue at all and got my word wall.
Anything I should watch out so I do not miss any words?
Missable here means you have one, or limited chance to get the word. After that you can't revisit the dungeon to look for it.