Here's how they are similar:
Homonyms share the same pronunciation, and the same can be said about Polysemes. Here's how they differ:
Polysemes share a concept; homonyms don't.
: different concepts
Here's an analogy. There are two rivers, one in the US and one in the UK. Both rivers sound the same, and they might even look the same, but they are not one and the same river. They have different origins; i.e., concepts.
bank (meaning, financial institute) comes from Old Italian banca.
bank (edge of a river) comes from Old Norse banki.Polyseme
: similar concept
Here's another analogy. There is one river, and it branches out, divides itself, multiplies itself into other rivers, all of which share the same origin;i.e., concept.
bank (meaning, financial institute) and bank (to put confidence in) both come from Old Italian banca.Bank on
(verb) means, rely on
, count on
. For example, You can bank on Molly's caterer to do a good job
. This expression alludes to bank as a reliable storage place for money.
Does that help so far?