Question

What is the difference of multimeric proteins with multisubunit proteins?

Answer 1

It is an imprecise and subjective difference in wording.

"Meric" tends to refer to proteins where the subunits are identical or nearly identical to each other. Like octomer would be 8 nearly identical subunits making up a protein. Where in multisubunit proteins the individual subunits can have any unrelated shapes under the sun. That's my interpretation. It's an excellent question and at the end of the day comes down to a mere difference in wording.