my %replacements = qw/men     women
                      houses  homes
                      cats    dogs
                      venus   mars
                      carpet  rug
                      full    empty/;

my $string = "men cats houses venus carpet full";

for my $keyword ( keys %replacements ) {
    my $re = qr/\b$keyword\b/;
    $string =~ s/$re/$replacements{$keyword}/gi;
}
print "$string\n";

__OUTPUT__
women dogs homes mars rugs empty