which is which
What particular one is what particular one, or what is the difference between different ones. For example, These twins look so much alike I can't tell which is which, or Both our raincoats are tan; do you know which is which? This idiom was first recorded about 1412.
| an extraordinary or unusual thing, person, or event; an exceptional example or instance. |
| a gadget; dingus; thingumbob. |
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