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GabrielP, you will find this forum much more useful if you do the initial research yourself by checking dictionaries and grammar textbooks. If there is something about the definition or usage of a word that you do not understand after doing that, then please ask us to help, and explain what it is that you do not understand.
"An hour" is correct. It starts with a vowel sound. (We pronounce "hour" with a silent "h", as if it were spelt "our".) Also, "It's anhonour." But if a word starts with an "h" sound, use "a". (Eg., "It was a hilarious comedy.")
This is often good advice, OD, but the answer to Gabriel's question is not easy for many learners to find. Most dictionaries give a phonemic transcription of the word, but learners may not make the necessary connection.