obedience -|-  

octopus -|- octo means 8, and octopus has 8 legs.  

official -|- The root word is ‘office', so to add the suffix, your drop the –e and add the suffix –ial.  

often -|- Like mortgage, the –t is there but not pronounced.  

oneself -|- Yet another word made up of 2 words. Same as nowadays, oneself is always one words when used together.  

opportunity -|- 2 O's and 1 U.  

original -|- From the root word origin, all an –al to make it an adjective.  

overrun -|- Don't run over the spelling of this word, combine the words over and run and make it one word, overrun.  

occasion -|- There is no need for an Ass in Occasion.  

occur -|- The C's in this word are the only letters that occurs twice. 

omission -|-   The book has many serious and significant omissions. 

outrageous -|- Spelling this word any different would be outrageous. Keep the outrage and add an -ous.