And on top of that, one word has two pronunciations: “route” with Long-U and “route” with Vowel /au/.
So, the best advice for [ou] is, first, to learn the correct pronunciation for all of the words here, so that you are confident with these ones. Then, for any new words with [ou] that you find in the future, be ready to listen carefully to the vowel sound.
A vowel pair is two vowel letters together, that make just one sound. For example, in the words “each” and “fear” the [ea] makes just one vowel sound, so this is a vowel pair. However, in “idea” and “create” the [ea] is not a vowel pair – there are two vowel sounds, and those two sounds are in different syllables.
Pronouncing vowel pairs
When you see a new word with a vowel pair, how can you know how to pronounce it?
Usually, the first vowel of the pair is the one that is pronounced, and it is usually with the long vowel sound for that letter. The second vowel is silent. For example: wait (Long-A), team (Long-E), people (Long-E), boat (Long-O), fruit (Long-U).
Sometimes, but less often, the first vowel in the pair uses its short vowel sound. For example: cause (Short-a-2), laugh (Short-a-1), ready (Short-e), sieve (Short-i).
There are some words in which the second vowel is the one that is pronounced. In these cases, it is most often with the long vowel sound. For example: aisle (Long-I), break (Long-A), piece (Long-E), neutral (Long-U), geyser (Long-I/Y), few (Long-U/W).
The least common pattern is when the second vowel is pronounced with its short vowel sound. For example: friend (Short-e), forfeit (Short-i), build (Short-i), because (Short-u).
So remember, in a vowel pair, just one of the vowels is pronounced, and the other is silent. And if you see a new word with a vowel pair, but you are not sure how to say it, the best thing to try first is the long sound of the first vowel.
There is only just a handful of words with a vowel pair that has a sound that is completely different from one of the letters in the pair. Some of them are: aura (Long-O); vein, eight, weigh, their, they (Long-A); said, says, again (Short-e); been (Short-i); sew (Long-O).
Also, there is one combination, [oi] or [oy], in which the sound of both vowels is heard and they stay together in the same syllable. Some examples are: boy, choice, coin, enjoy, point, voice.
Finally, there is one combination which has several pronunciations, and it is not easy to predict: [ou]. When you see a word with [ou], the best advice is to check a dictionary or ask a native speaker how to say it.