use warnings;
use strict;
use Data::Dumper;

my $line = "X\tN";
my @tags = split /\t/, $line;
my @Definition=("A", "NN", "B", "NNS", "YN", "ZX");
my @out = grep($_ =~ /^$tags[1]/, @Definition);
print Dumper(\@out);

__END__

$VAR1 = [
          'NN',
          'NNS'
        ];