The first discussion of flattening had to do with a list of data being flattened into an array.
Further down we see another different use of the word "flattening" : <quote src=http://dev.perl.org/perl6/synopsis/S06.html section="Flattening lists"> The unary prefix operator * flattens its operand (which allows the elements of an array or iterator to be used as an argument list). </quote> Here I understand this to mean that the array is spreading or distributing its elements to individual scalars. So, to avoid confusion with the common understanding of flattening in Perl, perhaps it should be called spreading or distributing.