The word "multiset" sounds too technical for what it is.
Dijkstra's "bag," on the other hand, doesn't sound technical enough.
https://math.stackexchange.com/questions/152223/why-does-mathematical-convention-deal-so-ineptly-with-multisets

A bag is a multiset. I insist on and promote bag because it is shorter, E. W. Dijkstra uses it, and submultiset is downright ugly.

http://www.cs.utoronto.ca/~trebla/subbag-sum.html

Why does mathematical convention deal so ineptly with multisets?

Many statements of mathematics are phrased most naturally in terms of multisets. For example: Every positive integer can be uniquely expressed as the product of a multiset of primes. But this th...

^{Mathematics Stack Exchange}