A homonym is a word that is spelled the same as another word, but has a different meaning.
Or, it can be words that sound the same but as spelled differently.
They may or may not have different pronunciations, but they usually come in pairs. For example, the word minute is a good word. Most of the time, a minute is a noun referring to 60 seconds of time. Sixty minutes make up an hour.
With this pronunciation, the emphasis is on the first syllable. However, minute can also be an adjective having nothing to do with time. When it is pronounced with the emphasis on the second syllable, it is an adjective that means very small (for example, a minute amount of poison can still affect you). For words that sound the same but are spelled differently, a great example is you’re and your.
For the above phrases, I am not sure what you mean. Phrases do not have homonyms, but this is my best guess as to what you are looking for:
Happening only has one pronunciation, but it can either be the -ing form of happen (This event is happening tonight) or a noun (There will be a big happening in the park tomorrow night). However, these meanings are not distinct enough to be homonyms.
In the second phrase, the word show is a homonym. It is pronounced the same way for both the verb and noun definitions, but they are quite different. If you go to see a show, you are going to attend a performance. Whether it is an animal show or musical show, you can sit in the audience and observe. If you want to show someone something, it means that you bring them to it and let them see, or you demonstrate something. See the different usages of show below:
- I want to show you this great new language learning app that I found. (verb)
- The light show that we saw last night was absolutely amazing! (noun)
Note that these are similar but quite distinct. Because of that, show is considered a homonym.