I found some characters, that look extremely similar to each other, like
|于||yu2||(surname), in/at/to/from/by/than/out of|
|千||qian1||thousand, a swing|
|干||gan1/gan4||dry/to concern/shield, to work/to do/to manage, manage/stem|
Is this a real language phenomenon? What is the name of it? Can I get a list of such "homonim sets"?