Miscellaneous sounds like it has a Latin root, but which one(s) is not immediately obvious. After some thought I came up with misc- meaning, I guess, "mix", as in miscible (two fluids are miscible if they will mix, or immiscible if, like oil and water, they won't). It sounds like the English mix may in fact be descended from that root too. Let's check and see if this is right...
So according to the American Heritage Dictionary miscellaneous comes from the Latin miscellus, "mixed". This comes from the verb miscēre, to mix.
Searching about suggests that all these words descend from this root: miscellaneous, miscible, miscegenation; also the French melee (mixed-up combat) and mélange (a mixed collection, a miscellany); also meddle (through Old French->Middle English). It seems that mix itself evolved somewhat differently from the rest, deriving from the Latin mixtus, the past participle of miscēre, which eventually arrived in Middle English as mixt/mixed, from which mix was derived as a back-formation.
Altogether this is a broader family of words than I would have guessed!