#!/usr/bin/perl
use strict;
use warnings;

my $h = {
    word1 => [ ('a' .. 'c') ],
    word2 => [ ('d' .. 'f') ],
};
push @{ $h->{word1} }, $h->{word2};

for my $word ( sort keys %$h ) {
    print "$word :\t";
    for my $letter ( @{ $h->{$word} } ) {
       print ref $letter eq 'ARRAY' ? @$letter : $letter;
    }
    print "\n";
}