It will be easier and most probably more efficient to store your words in a hash and check for existence of your candidates in the hash.

Something like this:

my $word = "of";
my %stopwords = map { $_ => 1 } qw/ a the of /;
if (exists $stopwords{$word}) {
   print "Stopword $word discarded\n";
}
else{
   print "$word is not a stop word\n";
}
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