my @S=("tilly","zaxo","sauog","enlil","castaway","wufnik");
my @U = ("castaway","zaxo","wufnik","enlil");

my %uS = map { $tmp = $_; $tmp => grep { $S[$_] =~ /^$tmp$/ } (0..$#S) } @U;

@uS = sort { $uS{$a} <=> $uS{$b} } @U;
print join "\n", @uS;