Actually for fast lookup you would be better using a hash than an array. Something like this populates a hash from a file (substitute your file handle for DATA):

use warnings;
use strict;

my %banned;

@banned{do {local $/; split ' ', <DATA>}} = ();
print join "\n", keys %banned;

my $word = 'porn';
print "\n\n$word is on the banned list\n" if exists $banned{$word};

__DATA__
p0rn viagra phetnermine online poker
casino porn
[download]

Prints:

casino
poker
phetnermine
viagra
p0rn
porn
online

porn is on the banned list
[download]