Correct spelling

opening

Correct spelling, explanation: opening is a gerund/present participle form of the verb open. As you can see, there’s no extra consonant in the basic word. Even if we wanted to double a consonant due to the rule that when there’s a single vowel before the last (and stressed as well) consonant in a word, we need to double that consonant, it should’ve been -n letter (but it’s not stressed, so this rule doesn’t apply here). The only correct version of this word is opening, not oppening.

Definition of opening:
1. noun (gerund), an act of moving something from a closed position
Opening this museum was really important to us.
We were worried about an opening of this school year.
2. verb (the present participle), moving something to see the inside
She was opening this door forever! I got tired from waiting.
My father is opening her eyes right now.

Collocations and phrasal verbs with opening:
Some most commonly used collocations and phrasal verbs include: opening up, opening a can of worms, and opening something a crack.


Incorrect spelling

oppening

Incorrect spelling, explanation: when we make a derivative of a word, we should always consider how its basic form is structured. In this case, it is the verb open. As we can easily see, there is no double consonant in it. That is why oppening is just a plain mistake, and the correct spelling is opening.

Incorrect spelling

openning

Incorrect spelling