Correct spelling, explanation: opinion is a noun that originates from Old French opinion (meaning opinion, view, judgments founded upon probabilities – 12c.) and from Latin opinionem (nominative opinio) opinion, conjecture. It first appeared in the early 14th century. As you can see, nothing in the history of this word indicates that it should be spelled with the double -p. The only correct version is opinion, not oppinion.

Definition of opinion:
noun, a thought or belief about something or someone
People tend to have strong opinions on controversial topics.
What’s your opinion about the matter?

Collocations with opinion:
Some most commonly used collocations include: honest opinion, negative opinion, and different opinion.
In my honest opinion, no one should justify violence.
I have a negative opinion of this restaurant. I didn’t like the food.
The fact that I have a different opinion than you doesn’t mean that I don’t like you.

Incorrect spelling, explanation: it is quite easy to spell the word opinion: it doesn’t contain any double vowels or double consonants. Some people, however, make the mistake of writing it with the double -p, which has no etymological explanation. This word comes from Old French opinion. Remember that the only correct form is opinion, not oppinion.

Incorrect spelling