Learn English – Why is anime not spelt phonetically

pro-NOUN-ciation is universally wrong. Even the highly permissive Merriam-Webster dictionary marks it with an obelus (÷). Here is what they say about pronunciations marked with an obelus:

The obelus, or division sign, is placed before a pronunciation variant that occurs in educated speech but that is considered by some to be questionable or unacceptable. This symbol is used sparingly and primarily for variants that have been objected to over a period of time in print by commentators on usage, in schools by teachers, or in correspondence that has come to the Merriam-Webster editorial department. In most cases the objection is based on orthographic or etymological arguments. (source)

As for why the word pronounce has an O between the two N’s and pronunciation does not, it is unclear, but both words derive from French, pronunciation from pronunciation and pronounce from pronuncier. There is probably some variation in the way the different word stress affected how the words were spelled after being borrowed into English.

Personal experience: It's not. Primer is pronounced with a long i sound, like miner or buyer, and I've never heard it ever pronounced differently.

Linguistic answer: Dictionaries vary on which is the correct pronunciation, but the OED, which is generally considered the final word on the English language, accepts both pronunciations as valid. The "long i" pronunciation occurs in etymologically related words such as primary and prime.

The short i pronunciation doesn't seem to be predominant (at least not in Southern California), so that's why we stick with the single "m".