Merriam-Webster's Official Scrabble Players Dictionary is the official tournament and club list of acceptable Scrabble words. It lists playable words that contain 2 - 8 letters. The word condition is not in the "official" dictionary because it contains 9 letters.
No. Eariest is not an acceptable Scrabble word.
No. Wop is not an acceptable Scrabble word.
No. Fo is not an acceptable Scrabble word.
Yes, "nus" is an acceptable word in Scrabble.
Yes. Moot is an acceptable Scrabble word.
No. Excelsis is not an acceptable Scrabble word.
No. Viz is not an acceptable Scrabble word.
No. Cie is not an acceptable Scrabble word.
Abbreviations are not acceptable in Scrabble.
In my eyes yes RN is an acceptable scrabble word.
Yes. Jo is an acceptable Scrabble word.
Yes. Re is an acceptable Scrabble word.