door
(as my first word, so hello guys)
wheels (warn me if i cheat, i can't remember all the words, we're at 70 already :-|)
light (finger crossed, hope it hasn't been said yet)
errm.
pluto
((what? message too short :s. oh well))
PS: btw, where's the other posting game of changing a letter, has it been removed? - nvm, it's been removed indeed.
terrestrial
hmm, uranus isn't terrestrial, it's a gaz giant. but anyways, pluto is not even a planet
thought someone should have noticed
--ohhh i got it, 'the opposite' 
so my word is:
EARTH