I second 2teez's question about using a CSV module to parse your file. Given this, here's one option:

use strict;
use warnings;
use Text::CSV;

my $csvFile = 'irregular-verbs.csv';
my $outFile = 'new.htm';

open my $outFH, '>', $outFile or die "Cannot open $outFile: $!";

my $csv = Text::CSV_XS->new( { binary => 1, auto_diag => 2 } )
  or die "Cannot use CSV: " . Text::CSV->error_diag();

open my $csvFH, '<', $csvFile or die "Cannot open $csvFile: $!";

# $row contains an array reference to the parsed csv line's data
while ( my $row = $csv->getline($csvFH) ) {
    print $outFH '<tr>';
    print $outFH "<td>$_</td>" for @$row;
    print $outFH "<tr>\n";
}

close $csvFH;
close $outFH;
[download]

Output to file:

<tr><td>Base Form</td><td>Past Simple</td><td>Past Participle</td><td>
+3rd Person Singular</td><td>Present Participle / Gerund</td><tr>
<tr><td>Abide</td><td>Abode/Abided</td><td>Abode/Abided/Abidden</td><t
+d>Abides</td><td>Abiding</td><tr>
<tr><td>Aby/Abye</td><td>Abought</td><td>Abought</td><td>Abys/Abyes</t
+d><td>Abying</td><tr>
<tr><td>Alight</td><td>Alit/Alighted</td><td>Alit/Alighted</td><td>Ali
+ghts</td><td>Alighting</td><tr>
<tr><td>Arise</td><td>Arose</td><td>Arisen</td><td>Arises</td><td>Aris
+ing</td><tr>
<tr><td>Awake</td><td>Awoke</td><td>Awoken</td><td>Awakes</td><td>Awak
+ing</td><tr>
[download]

Hope this helps!