Seiyuu - This is the one that really annoys me. Seiyuu is the proper word for "voice actor" in Japanese, so as soon as a voice actor comes from Japan, he or she is not a voice actor in English terms, they're "Seiyuu" instead. Doesn't make sense; they're actors who provide voices, so they're voice actors. Which English words did "seiyuu" derive from?
I don't believe any, since it's a Japanese word. In general, I see Seiyuu used when referring to Japanese voice actors, and Voice Actor or VA for English voice actors or otherwise. For example: "Jade Curtiss: Seiyuu: Takehito Koyasu. Voice Actor: Kirk Thornton" (Not the best example, but you get the idea). I personally just use the term 'voice actor'.

Anime - A word I assume to be derived from the way they write "animation" in transliterated Japanese. They're still charicatures animated by overlaying cells and indivually drawn frames, so how is it not still a cartoon? Why do we have to use the word "anime" just because it's from Japan and uses their drawing style? A sponge cake that's light brown and has strawberry jam in the middle may be called a Victoria Sandwich, but everyone still just calls it cake.
This is actually rather humorous because in Japanese, Anime (which you're right, it is short for animation) refers to all types of animation, not just Japanese animation. But in English and in other languages it's come to refer to specifically Japanese animation. Go figure.