multiple = opposite of singular = more than 1 (often very few, like only 2 or 3, but also often a lot more, like 10 or 20! it's very non-specific) a multitude = a lot = lots = usually more than just a few ... it's usually not a small amount, but not strictly - it can potentially be a small number, but that's rare

The word multitude is a noun, but the word multiple could be an adjective or a noun. For example, we say ' a multitude (noun) of stars,' and by that, we mean a very large number of stars, but we say ' multiple (used as an adjective) stars', and by that, we mean many stars. Also multiple as a noun is a mathematical term meaning a number that can be produced by multiplying a smaller number. for example, we say: 35 is a multiple of 7. So, it is wrong to say ' a multiple of something'.

Multiple vs. multitude The main difference between them is that they are different parts of speech. Multiple is an adjective and shall be used to describe nouns. For example: multiple versions multiple entries multiple instances Multitude, on the other hand, is a noun. You can't use multitude to describe a noun. For example: a multitude of problems. As for shortfall and deficit, they sort of mean the same thing but have different connotations. For shortfall, you are expecting a certain number/ result but it was not met or achieved. With deficit, like shortfall, there is also a lack or shortage of something, but it does not imply whether that result was expected or not. I hope you understood my explanation!